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 $57.36   9.188%   $62.6302   $62.63   $62.65   $62.60  
  Purchase #2 $95.92   5.692%   $101.3798   $101.38   $101.40   $101.40  
  Purchase #3 $164.61   4.546%   $172.0932   $172.09   $172.10   $172.10  
  Purchase #4 $237.28   5.506%   $250.3446   $250.34   $250.35   $250.30  
  Purchase #5 $88.63   10.139%   $97.6162   $97.62   $97.60   $97.60  
  Purchase #6 $91.41   3.595%   $94.6962   $94.70   $94.70   $94.70  
  Purchase #7 $156.70   3.365%   $161.973   $161.97   $161.95   $162.00  
  7 purchase totals = $891.91       $940.7332   $940.73   $940.75   $940.70