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 $46.97   6.246%   $49.9037   $49.90   $49.90   $49.90  
  Purchase #2 $202.67   10.672%   $224.2989   $224.30   $224.30   $224.30  
  Purchase #3 $146.91   13.118%   $166.1817   $166.18   $166.20   $166.20  
  Purchase #4 $72.93   5.580%   $76.9995   $77.00   $77.00   $77.00  
  Purchase #5 $131.81   11.172%   $146.5358   $146.54   $146.55   $146.50  
  Purchase #6 $34.76   3.874%   $36.1066   $36.11   $36.10   $36.10  
  Purchase #7 $51.29   5.355%   $54.0366   $54.04   $54.05   $54.00  
  7 purchase totals = $687.34       $754.0628   $754.07   $754.10   $754.00