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 $54.56   10.186%   $60.1175   $60.12   $60.10   $60.10  
  Purchase #2 $127.77   5.463%   $134.7501   $134.75   $134.75   $134.80  
  Purchase #3 $91.74   3.554%   $95.0004   $95.00   $95.00   $95.00  
  Purchase #4 $66.30   4.496%   $69.2808   $69.28   $69.30   $69.30  
  Purchase #5 $221.61   3.522%   $229.4151   $229.42   $229.40   $229.40  
  Purchase #6 $95.62   13.340%   $108.3757   $108.38   $108.40   $108.40  
  Purchase #7 $88.38   10.619%   $97.7651   $97.77   $97.75   $97.80  
  7 purchase totals = $745.98       $794.7047   $794.72   $794.70   $794.80