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 $68.66   6.152%   $72.884   $72.88   $72.90   $72.90  
  Purchase #2 $148.88   6.517%   $158.5825   $158.58   $158.60   $158.60  
  Purchase #3 $46.61   5.687%   $49.2607   $49.26   $49.25   $49.30  
  Purchase #4 $151.38   10.541%   $167.337   $167.34   $167.35   $167.30  
  Purchase #5 $64.29   13.826%   $73.1787   $73.18   $73.20   $73.20  
  Purchase #6 $220.74   9.529%   $241.7743   $241.77   $241.75   $241.80  
  Purchase #7 $164.48   12.427%   $184.9199   $184.92   $184.90   $184.90  
  7 purchase totals = $865.04       $947.9371   $947.93   $947.95   $948.00