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 $229.49   11.351%   $255.5394   $255.54   $255.55   $255.50  
  Purchase #2 $211.43   11.704%   $236.1758   $236.18   $236.20   $236.20  
  Purchase #3 $170.88   9.330%   $186.8231   $186.82   $186.80   $186.80  
  Purchase #4 $154.56   7.633%   $166.3576   $166.36   $166.35   $166.40  
  Purchase #5 $33.86   9.177%   $36.9673   $36.97   $36.95   $37.00  
  Purchase #6 $159.29   9.808%   $174.9132   $174.91   $174.90   $174.90  
  Purchase #7 $133.68   11.845%   $149.5144   $149.51   $149.50   $149.50  
  7 purchase totals = $1,093.19       $1,206.2908   $1,206.29   $1,206.25   $1,206.30