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 $223.91   12.556%   $252.0241   $252.02   $252.00   $252.00  
  Purchase #2 $33.65   7.739%   $36.2542   $36.25   $36.25   $36.30  
  Purchase #3 $41.95   13.422%   $47.5805   $47.58   $47.60   $47.60  
  Purchase #4 $178.40   12.105%   $199.9953   $200.00   $200.00   $200.00  
  Purchase #5 $100.89   3.132%   $104.0499   $104.05   $104.05   $104.00  
  Purchase #6 $85.44   8.694%   $92.8682   $92.87   $92.85   $92.90  
  Purchase #7 $27.32   3.305%   $28.2229   $28.22   $28.20   $28.20  
  7 purchase totals = $691.56       $760.9951   $760.99   $760.95   $761.00