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 $187.47   8.282%   $202.9963   $203.00   $203.00   $203.00  
  Purchase #2 $244.58   10.539%   $270.3563   $270.36   $270.35   $270.40  
  Purchase #3 $131.26   11.749%   $146.6817   $146.68   $146.70   $146.70  
  Purchase #4 $72.57   4.125%   $75.5635   $75.56   $75.55   $75.60  
  Purchase #5 $46.92   5.766%   $49.6254   $49.63   $49.65   $49.60  
  Purchase #6 $161.94   13.354%   $183.5655   $183.57   $183.55   $183.60  
  Purchase #7 $5.25   13.862%   $5.9778   $5.98   $6.00   $6.00  
  7 purchase totals = $849.99       $934.7665   $934.78   $934.80   $934.90