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 $59.60   12.452%   $67.0214   $67.02   $67.00   $67.00  
  Purchase #2 $26.37   13.281%   $29.8722   $29.87   $29.85   $29.90  
  Purchase #3 $67.65   4.855%   $70.9344   $70.93   $70.95   $70.90  
  Purchase #4 $234.68   10.348%   $258.9647   $258.96   $258.95   $259.00  
  Purchase #5 $215.71   13.288%   $244.3735   $244.37   $244.35   $244.40  
  Purchase #6 $146.34   4.853%   $153.4419   $153.44   $153.45   $153.40  
  Purchase #7 $78.36   5.681%   $82.8116   $82.81   $82.80   $82.80  
  7 purchase totals = $828.71       $907.4197   $907.40   $907.35   $907.40