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 $57.64   12.302%   $64.7309   $64.73   $64.75   $64.70  
  Purchase #2 $180.98   8.247%   $195.9054   $195.91   $195.90   $195.90  
  Purchase #3 $48.43   12.579%   $54.522   $54.52   $54.50   $54.50  
  Purchase #4 $164.77   9.315%   $180.1183   $180.12   $180.10   $180.10  
  Purchase #5 $176.46   3.218%   $182.1385   $182.14   $182.15   $182.10  
  Purchase #6 $151.76   11.668%   $169.4674   $169.47   $169.45   $169.50  
  Purchase #7 $126.57   8.450%   $137.2652   $137.27   $137.25   $137.30  
  7 purchase totals = $906.61       $984.1477   $984.16   $984.10   $984.10