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 $233.95   8.485%   $253.8007   $253.80   $253.80   $253.80  
  Purchase #2 $99.90   13.665%   $113.5513   $113.55   $113.55   $113.60  
  Purchase #3 $171.38   3.522%   $177.416   $177.42   $177.40   $177.40  
  Purchase #4 $15.40   8.593%   $16.7233   $16.72   $16.70   $16.70  
  Purchase #5 $119.76   9.662%   $131.3312   $131.33   $131.35   $131.30  
  Purchase #6 $245.59   6.105%   $260.5833   $260.58   $260.60   $260.60  
  Purchase #7 $97.83   3.853%   $101.5994   $101.60   $101.60   $101.60  
  7 purchase totals = $983.81       $1,055.0052   $1,055.00   $1,055.00   $1,055.00