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 $210.56   12.369%   $236.6042   $236.60   $236.60   $236.60  
  Purchase #2 $57.68   9.103%   $62.9306   $62.93   $62.95   $62.90  
  Purchase #3 $44.58   10.240%   $49.145   $49.15   $49.15   $49.10  
  Purchase #4 $34.75   10.289%   $38.3254   $38.33   $38.35   $38.30  
  Purchase #5 $75.96   8.285%   $82.2533   $82.25   $82.25   $82.30  
  Purchase #6 $94.38   3.812%   $97.9778   $97.98   $98.00   $98.00  
  Purchase #7 $145.37   6.541%   $154.8787   $154.88   $154.90   $154.90  
  7 purchase totals = $663.28       $722.1150   $722.12   $722.20   $722.10