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 $74.44   11.745%   $83.183   $83.18   $83.20   $83.20  
  Purchase #2 $213.40   6.545%   $227.367   $227.37   $227.35   $227.40  
  Purchase #3 $43.28   11.779%   $48.378   $48.38   $48.40   $48.40  
  Purchase #4 $85.90   13.745%   $97.707   $97.71   $97.70   $97.70  
  Purchase #5 $109.98   10.800%   $121.8578   $121.86   $121.85   $121.90  
  Purchase #6 $34.39   10.560%   $38.0216   $38.02   $38.00   $38.00  
  Purchase #7 $192.35   11.837%   $215.1185   $215.12   $215.10   $215.10  
  7 purchase totals = $753.74       $831.6329   $831.64   $831.60   $831.70