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 $60.80   11.406%   $67.7348   $67.73   $67.75   $67.70  
  Purchase #2 $75.87   3.738%   $78.706   $78.71   $78.70   $78.70  
  Purchase #3 $170.59   6.858%   $182.2891   $182.29   $182.30   $182.30  
  Purchase #4 $82.28   12.272%   $92.3774   $92.38   $92.40   $92.40  
  Purchase #5 $197.91   5.847%   $209.4818   $209.48   $209.50   $209.50  
  Purchase #6 $245.25   10.840%   $271.8351   $271.84   $271.85   $271.80  
  Purchase #7 $23.35   9.464%   $25.5598   $25.56   $25.55   $25.60  
  7 purchase totals = $856.05       $927.9840   $927.99   $928.05   $928.00