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 $31.61   9.292%   $34.5472   $34.55   $34.55   $34.50  
  Purchase #2 $215.85   11.284%   $240.2065   $240.21   $240.20   $240.20  
  Purchase #3 $26.39   3.627%   $27.3472   $27.35   $27.35   $27.30  
  Purchase #4 $81.34   11.604%   $90.7787   $90.78   $90.80   $90.80  
  Purchase #5 $103.89   13.458%   $117.8715   $117.87   $117.85   $117.90  
  Purchase #6 $158.96   12.389%   $178.6536   $178.65   $178.65   $178.70  
  Purchase #7 $149.99   8.491%   $162.7257   $162.73   $162.75   $162.70  
  7 purchase totals = $768.03       $852.1304   $852.14   $852.15   $852.10