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 $134.95   12.361%   $151.6312   $151.63   $151.65   $151.60  
  Purchase #2 $92.98   5.684%   $98.265   $98.27   $98.25   $98.30  
  Purchase #3 $13.66   4.119%   $14.2227   $14.22   $14.20   $14.20  
  Purchase #4 $171.45   11.543%   $191.2405   $191.24   $191.25   $191.20  
  Purchase #5 $129.50   8.634%   $140.681   $140.68   $140.70   $140.70  
  Purchase #6 $244.26   5.131%   $256.793   $256.79   $256.80   $256.80  
  Purchase #7 $49.32   9.599%   $54.0542   $54.05   $54.05   $54.10  
  7 purchase totals = $836.12       $906.8876   $906.88   $906.90   $906.90