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 $73.77   12.750%   $83.1757   $83.18   $83.20   $83.20  
  Purchase #2 $156.46   13.742%   $177.9607   $177.96   $177.95   $178.00  
  Purchase #3 $46.47   13.401%   $52.6974   $52.70   $52.70   $52.70  
  Purchase #4 $138.51   5.461%   $146.074   $146.07   $146.05   $146.10  
  Purchase #5 $195.41   6.504%   $208.1195   $208.12   $208.10   $208.10  
  Purchase #6 $244.82   12.607%   $275.6845   $275.68   $275.70   $275.70  
  Purchase #7 $11.81   5.553%   $12.4658   $12.47   $12.45   $12.50  
  7 purchase totals = $867.25       $956.1776   $956.18   $956.15   $956.30