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 $92.63   4.225%   $96.5436   $96.54   $96.55   $96.50  
  Purchase #2 $131.56   5.858%   $139.2668   $139.27   $139.25   $139.30  
  Purchase #3 $112.26   11.748%   $125.4483   $125.45   $125.45   $125.40  
  Purchase #4 $236.72   13.841%   $269.4844   $269.48   $269.50   $269.50  
  Purchase #5 $173.96   11.672%   $194.2646   $194.26   $194.25   $194.30  
  Purchase #6 $69.59   3.832%   $72.2567   $72.26   $72.25   $72.30  
  Purchase #7 $94.99   6.707%   $101.361   $101.36   $101.35   $101.40  
  7 purchase totals = $911.71       $998.6254   $998.62   $998.60   $998.70