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 $225.88   12.376%   $253.8349   $253.83   $253.85   $253.80  
  Purchase #2 $191.81   8.184%   $207.5077   $207.51   $207.50   $207.50  
  Purchase #3 $150.49   4.787%   $157.694   $157.69   $157.70   $157.70  
  Purchase #4 $104.85   5.123%   $110.2215   $110.22   $110.20   $110.20  
  Purchase #5 $69.34   5.703%   $73.2945   $73.29   $73.30   $73.30  
  Purchase #6 $112.77   8.387%   $122.228   $122.23   $122.25   $122.20  
  Purchase #7 $107.27   3.210%   $110.7134   $110.71   $110.70   $110.70  
  7 purchase totals = $962.41       $1,035.4940   $1,035.48   $1,035.50   $1,035.40