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 $102.82   11.811%   $114.9641   $114.96   $114.95   $115.00  
  Purchase #2 $162.73   9.240%   $177.7663   $177.77   $177.75   $177.80  
  Purchase #3 $91.35   6.548%   $97.3316   $97.33   $97.35   $97.30  
  Purchase #4 $32.76   5.599%   $34.5942   $34.59   $34.60   $34.60  
  Purchase #5 $109.55   7.188%   $117.4245   $117.42   $117.40   $117.40  
  Purchase #6 $18.34   5.306%   $19.3131   $19.31   $19.30   $19.30  
  Purchase #7 $32.80   9.331%   $35.8606   $35.86   $35.85   $35.90  
  7 purchase totals = $550.35       $597.2544   $597.24   $597.20   $597.30