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 $212.55   13.446%   $241.1295   $241.13   $241.15   $241.10  
  Purchase #2 $111.76   5.131%   $117.4944   $117.49   $117.50   $117.50  
  Purchase #3 $83.83   10.872%   $92.944   $92.94   $92.95   $92.90  
  Purchase #4 $34.73   4.108%   $36.1567   $36.16   $36.15   $36.20  
  Purchase #5 $59.57   4.845%   $62.4562   $62.46   $62.45   $62.50  
  Purchase #6 $209.26   12.777%   $235.9972   $236.00   $236.00   $236.00  
  Purchase #7 $15.83   3.846%   $16.4388   $16.44   $16.45   $16.40  
  7 purchase totals = $727.53       $802.6168   $802.62   $802.65   $802.60