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 $43.81   7.173%   $46.9525   $46.95   $46.95   $47.00  
  Purchase #2 $124.65   8.494%   $135.2378   $135.24   $135.25   $135.20  
  Purchase #3 $35.31   13.690%   $40.1439   $40.14   $40.15   $40.10  
  Purchase #4 $97.31   9.837%   $106.8824   $106.88   $106.90   $106.90  
  Purchase #5 $169.26   10.482%   $187.0018   $187.00   $187.00   $187.00  
  Purchase #6 $16.58   11.103%   $18.4209   $18.42   $18.40   $18.40  
  Purchase #7 $232.38   11.492%   $259.0851   $259.09   $259.10   $259.10  
  7 purchase totals = $719.30       $793.7244   $793.72   $793.75   $793.70