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 $208.99   8.472%   $226.6956   $226.70   $226.70   $226.70  
  Purchase #2 $233.84   6.848%   $249.8534   $249.85   $249.85   $249.90  
  Purchase #3 $178.89   5.339%   $188.4409   $188.44   $188.45   $188.40  
  Purchase #4 $182.99   6.776%   $195.3894   $195.39   $195.40   $195.40  
  Purchase #5 $168.60   5.352%   $177.6235   $177.62   $177.60   $177.60  
  Purchase #6 $94.89   10.410%   $104.768   $104.77   $104.75   $104.80  
  Purchase #7 $119.92   4.411%   $125.2097   $125.21   $125.20   $125.20  
  7 purchase totals = $1,188.12       $1,267.9805   $1,267.98   $1,267.95   $1,268.00