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 $191.66   7.271%   $205.5956   $205.60   $205.60   $205.60  
  Purchase #2 $103.75   13.685%   $117.9482   $117.95   $117.95   $117.90  
  Purchase #3 $22.77   11.512%   $25.3913   $25.39   $25.40   $25.40  
  Purchase #4 $49.38   6.862%   $52.7685   $52.77   $52.75   $52.80  
  Purchase #5 $221.54   5.126%   $232.8961   $232.90   $232.90   $232.90  
  Purchase #6 $209.28   7.605%   $225.1957   $225.20   $225.20   $225.20  
  Purchase #7 $92.33   4.573%   $96.5523   $96.55   $96.55   $96.60  
  7 purchase totals = $890.71       $956.3477   $956.36   $956.35   $956.40