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 $24.86   4.288%   $25.926   $25.93   $25.95   $25.90  
  Purchase #2 $132.59   9.651%   $145.3863   $145.39   $145.40   $145.40  
  Purchase #3 $184.68   11.681%   $206.2525   $206.25   $206.25   $206.30  
  Purchase #4 $131.28   11.517%   $146.3995   $146.40   $146.40   $146.40  
  Purchase #5 $128.73   7.131%   $137.9097   $137.91   $137.90   $137.90  
  Purchase #6 $159.50   6.142%   $169.2965   $169.30   $169.30   $169.30  
  Purchase #7 $116.74   3.837%   $121.2193   $121.22   $121.20   $121.20  
  7 purchase totals = $878.38       $952.3898   $952.40   $952.40   $952.40