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 $47.79   9.206%   $52.1895   $52.19   $52.20   $52.20  
  Purchase #2 $60.28   4.510%   $62.9986   $63.00   $63.00   $63.00  
  Purchase #3 $126.42   7.494%   $135.8939   $135.89   $135.90   $135.90  
  Purchase #4 $229.83   5.105%   $241.5628   $241.56   $241.55   $241.60  
  Purchase #5 $169.38   7.570%   $182.2021   $182.20   $182.20   $182.20  
  Purchase #6 $45.86   5.478%   $48.3722   $48.37   $48.35   $48.40  
  Purchase #7 $92.30   7.585%   $99.301   $99.30   $99.30   $99.30  
  7 purchase totals = $771.86       $822.5201   $822.51   $822.50   $822.60