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 $234.72   13.855%   $267.2405   $267.24   $267.25   $267.20  
  Purchase #2 $133.98   12.236%   $150.3738   $150.37   $150.35   $150.40  
  Purchase #3 $91.81   8.105%   $99.2512   $99.25   $99.25   $99.30  
  Purchase #4 $217.49   8.806%   $236.6422   $236.64   $236.65   $236.60  
  Purchase #5 $210.99   6.226%   $224.1262   $224.13   $224.15   $224.10  
  Purchase #6 $37.29   3.792%   $38.704   $38.70   $38.70   $38.70  
  Purchase #7 $105.51   13.187%   $119.4236   $119.42   $119.40   $119.40  
  7 purchase totals = $1,031.79       $1,135.7615   $1,135.75   $1,135.75   $1,135.70