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 $135.43   8.426%   $146.8413   $146.84   $146.85   $146.80  
  Purchase #2 $227.71   3.206%   $235.0104   $235.01   $235.00   $235.00  
  Purchase #3 $67.70   5.827%   $71.6449   $71.64   $71.65   $71.60  
  Purchase #4 $249.49   9.569%   $273.3637   $273.36   $273.35   $273.40  
  Purchase #5 $143.53   12.568%   $161.5689   $161.57   $161.55   $161.60  
  Purchase #6 $229.34   6.427%   $244.0797   $244.08   $244.10   $244.10  
  Purchase #7 $199.47   12.507%   $224.4177   $224.42   $224.40   $224.40  
  7 purchase totals = $1,252.67       $1,356.9266   $1,356.92   $1,356.90   $1,356.90