Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.28   5.347%   $151.9947   $151.99   $152.00   $152.00  
  Purchase #2 $108.86   7.422%   $116.9396   $116.94   $116.95   $116.90  
  Purchase #3 $170.87   11.163%   $189.9442   $189.94   $189.95   $189.90  
  Purchase #4 $243.72   5.611%   $257.3951   $257.40   $257.40   $257.40  
  Purchase #5 $231.83   12.363%   $260.4911   $260.49   $260.50   $260.50  
  Purchase #6 $248.60   7.352%   $266.8771   $266.88   $266.90   $266.90  
  Purchase #7 $173.50   5.286%   $182.6712   $182.67   $182.65   $182.70  
  7 purchase totals = $1,321.66       $1,426.3130   $1,426.31   $1,426.35   $1,426.30