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 $61.54   5.586%   $64.9776   $64.98   $65.00   $65.00  
  Purchase #2 $15.96   10.444%   $17.6269   $17.63   $17.65   $17.60  
  Purchase #3 $89.47   8.763%   $97.3103   $97.31   $97.30   $97.30  
  Purchase #4 $20.38   3.712%   $21.1365   $21.14   $21.15   $21.10  
  Purchase #5 $73.38   3.438%   $75.9028   $75.90   $75.90   $75.90  
  Purchase #6 $72.92   4.855%   $76.4603   $76.46   $76.45   $76.50  
  Purchase #7 $245.98   4.195%   $256.2989   $256.30   $256.30   $256.30  
  7 purchase totals = $579.63       $609.7133   $609.72   $609.75   $609.70