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 $59.28   13.664%   $67.38   $67.38   $67.40   $67.40  
  Purchase #2 $92.70   10.283%   $102.2323   $102.23   $102.25   $102.20  
  Purchase #3 $93.29   6.534%   $99.3856   $99.39   $99.40   $99.40  
  Purchase #4 $245.58   12.305%   $275.7986   $275.80   $275.80   $275.80  
  Purchase #5 $108.82   8.363%   $117.9206   $117.92   $117.90   $117.90  
  Purchase #6 $73.61   3.132%   $75.9155   $75.92   $75.90   $75.90  
  Purchase #7 $176.26   4.228%   $183.7123   $183.71   $183.70   $183.70  
  7 purchase totals = $849.54       $922.3449   $922.35   $922.35   $922.30