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 $108.36   5.260%   $114.0597   $114.06   $114.05   $114.10  
  Purchase #2 $133.69   4.432%   $139.6151   $139.62   $139.60   $139.60  
  Purchase #3 $86.70   11.714%   $96.856   $96.86   $96.85   $96.90  
  Purchase #4 $87.41   13.829%   $99.4979   $99.50   $99.50   $99.50  
  Purchase #5 $187.53   6.208%   $199.1719   $199.17   $199.15   $199.20  
  Purchase #6 $60.41   3.254%   $62.3757   $62.38   $62.40   $62.40  
  Purchase #7 $225.87   10.519%   $249.6293   $249.63   $249.65   $249.60  
  7 purchase totals = $889.97       $961.2056   $961.22   $961.20   $961.30