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 $22.49   8.376%   $24.3738   $24.37   $24.35   $24.40  
  Purchase #2 $93.68   6.240%   $99.5256   $99.53   $99.55   $99.50  
  Purchase #3 $55.54   12.769%   $62.6319   $62.63   $62.65   $62.60  
  Purchase #4 $171.78   6.732%   $183.3442   $183.34   $183.35   $183.30  
  Purchase #5 $78.32   12.763%   $88.316   $88.32   $88.30   $88.30  
  Purchase #6 $182.94   8.181%   $197.9063   $197.91   $197.90   $197.90  
  Purchase #7 $46.38   8.500%   $50.3223   $50.32   $50.30   $50.30  
  7 purchase totals = $651.13       $706.4201   $706.42   $706.40   $706.30