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 $106.88   7.577%   $114.9783   $114.98   $115.00   $115.00  
  Purchase #2 $18.95   3.267%   $19.5691   $19.57   $19.55   $19.60  
  Purchase #3 $60.47   8.406%   $65.5531   $65.55   $65.55   $65.60  
  Purchase #4 $134.43   7.404%   $144.3832   $144.38   $144.40   $144.40  
  Purchase #5 $155.42   4.461%   $162.3533   $162.35   $162.35   $162.40  
  Purchase #6 $215.81   9.510%   $236.3335   $236.33   $236.35   $236.30  
  Purchase #7 $223.42   8.843%   $243.177   $243.18   $243.20   $243.20  
  7 purchase totals = $915.38       $986.3475   $986.34   $986.40   $986.50