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 $105.98   9.725%   $116.2866   $116.29   $116.30   $116.30  
  Purchase #2 $250.91   10.354%   $276.8892   $276.89   $276.90   $276.90  
  Purchase #3 $218.88   12.804%   $246.9054   $246.91   $246.90   $246.90  
  Purchase #4 $70.61   5.248%   $74.3156   $74.32   $74.30   $74.30  
  Purchase #5 $59.37   3.643%   $61.5328   $61.53   $61.55   $61.50  
  Purchase #6 $194.96   3.711%   $202.195   $202.20   $202.20   $202.20  
  Purchase #7 $40.50   8.855%   $44.0863   $44.09   $44.10   $44.10  
  7 purchase totals = $941.21       $1,022.2109   $1,022.23   $1,022.25   $1,022.20