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 $241.90   5.816%   $255.9689   $255.97   $255.95   $256.00  
  Purchase #2 $47.48   10.815%   $52.615   $52.62   $52.60   $52.60  
  Purchase #3 $53.79   8.297%   $58.253   $58.25   $58.25   $58.30  
  Purchase #4 $72.34   4.266%   $75.426   $75.43   $75.45   $75.40  
  Purchase #5 $215.88   13.146%   $244.2596   $244.26   $244.25   $244.30  
  Purchase #6 $73.41   4.608%   $76.7927   $76.79   $76.80   $76.80  
  Purchase #7 $140.53   7.472%   $151.0304   $151.03   $151.05   $151.00  
  7 purchase totals = $845.33       $914.3456   $914.35   $914.35   $914.40