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 $230.67   13.428%   $261.6444   $261.64   $261.65   $261.60  
  Purchase #2 $194.90   6.572%   $207.7088   $207.71   $207.70   $207.70  
  Purchase #3 $221.95   6.732%   $236.8917   $236.89   $236.90   $236.90  
  Purchase #4 $43.32   13.548%   $49.189   $49.19   $49.20   $49.20  
  Purchase #5 $101.79   12.691%   $114.7082   $114.71   $114.70   $114.70  
  Purchase #6 $86.47   6.181%   $91.8147   $91.81   $91.80   $91.80  
  Purchase #7 $105.90   13.716%   $120.4252   $120.43   $120.45   $120.40  
  7 purchase totals = $985.00       $1,082.3820   $1,082.38   $1,082.40   $1,082.30