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 $55.56   12.643%   $62.5845   $62.58   $62.60   $62.60  
  Purchase #2 $48.75   6.132%   $51.7394   $51.74   $51.75   $51.70  
  Purchase #3 $85.98   7.627%   $92.5377   $92.54   $92.55   $92.50  
  Purchase #4 $41.92   12.619%   $47.2099   $47.21   $47.20   $47.20  
  Purchase #5 $92.95   11.745%   $103.867   $103.87   $103.85   $103.90  
  Purchase #6 $170.77   13.120%   $193.175   $193.18   $193.20   $193.20  
  Purchase #7 $229.34   12.390%   $257.7552   $257.76   $257.75   $257.80  
  7 purchase totals = $725.27       $808.8687   $808.88   $808.90   $808.90