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 $204.94   13.305%   $232.2073   $232.21   $232.20   $232.20  
  Purchase #2 $149.48   9.147%   $163.1529   $163.15   $163.15   $163.20  
  Purchase #3 $82.42   10.262%   $90.8779   $90.88   $90.90   $90.90  
  Purchase #4 $87.68   11.185%   $97.487   $97.49   $97.50   $97.50  
  Purchase #5 $215.95   8.637%   $234.6016   $234.60   $234.60   $234.60  
  Purchase #6 $200.50   8.426%   $217.3941   $217.39   $217.40   $217.40  
  Purchase #7 $227.86   4.330%   $237.7263   $237.73   $237.75   $237.70  
  7 purchase totals = $1,168.83       $1,273.4471   $1,273.45   $1,273.50   $1,273.50