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 $107.43   6.179%   $114.0681   $114.07   $114.05   $114.10  
  Purchase #2 $191.47   10.707%   $211.9707   $211.97   $211.95   $212.00  
  Purchase #3 $57.93   5.792%   $61.2853   $61.29   $61.30   $61.30  
  Purchase #4 $161.95   7.322%   $173.808   $173.81   $173.80   $173.80  
  Purchase #5 $238.87   8.238%   $258.5481   $258.55   $258.55   $258.50  
  Purchase #6 $193.93   11.117%   $215.4892   $215.49   $215.50   $215.50  
  Purchase #7 $216.40   10.431%   $238.9727   $238.97   $238.95   $239.00  
  7 purchase totals = $1,167.98       $1,274.1421   $1,274.15   $1,274.10   $1,274.20