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 $85.54   12.145%   $95.9288   $95.93   $95.95   $95.90  
  Purchase #2 $247.44   3.825%   $256.9046   $256.90   $256.90   $256.90  
  Purchase #3 $125.60   3.800%   $130.3728   $130.37   $130.35   $130.40  
  Purchase #4 $22.58   4.263%   $23.5426   $23.54   $23.55   $23.50  
  Purchase #5 $99.38   13.543%   $112.839   $112.84   $112.85   $112.80  
  Purchase #6 $236.69   8.867%   $257.6773   $257.68   $257.70   $257.70  
  Purchase #7 $32.47   10.762%   $35.9644   $35.96   $35.95   $36.00  
  7 purchase totals = $849.70       $913.2295   $913.22   $913.25   $913.20