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 $232.98   3.813%   $241.8635   $241.86   $241.85   $241.90  
  Purchase #2 $231.95   13.866%   $264.1122   $264.11   $264.10   $264.10  
  Purchase #3 $207.89   9.475%   $227.5876   $227.59   $227.60   $227.60  
  Purchase #4 $131.37   7.245%   $140.8878   $140.89   $140.90   $140.90  
  Purchase #5 $245.27   6.727%   $261.7693   $261.77   $261.75   $261.80  
  Purchase #6 $21.96   11.587%   $24.5045   $24.50   $24.50   $24.50  
  Purchase #7 $75.94   9.514%   $83.1649   $83.16   $83.15   $83.20  
  7 purchase totals = $1,147.36       $1,243.8898   $1,243.88   $1,243.85   $1,244.00