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 $209.42   12.756%   $236.1336   $236.13   $236.15   $236.10  
  Purchase #2 $233.40   4.352%   $243.5576   $243.56   $243.55   $243.60  
  Purchase #3 $32.49   13.454%   $36.8612   $36.86   $36.85   $36.90  
  Purchase #4 $182.87   9.646%   $200.5096   $200.51   $200.50   $200.50  
  Purchase #5 $54.84   5.231%   $57.7087   $57.71   $57.70   $57.70  
  Purchase #6 $67.69   13.741%   $76.9913   $76.99   $77.00   $77.00  
  Purchase #7 $131.89   6.447%   $140.3929   $140.39   $140.40   $140.40  
  7 purchase totals = $912.60       $992.1549   $992.15   $992.15   $992.20