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 $67.35   10.572%   $74.4702   $74.47   $74.45   $74.50  
  Purchase #2 $145.40   11.836%   $162.6095   $162.61   $162.60   $162.60  
  Purchase #3 $60.73   3.296%   $62.7317   $62.73   $62.75   $62.70  
  Purchase #4 $105.73   7.817%   $113.9949   $113.99   $114.00   $114.00  
  Purchase #5 $60.36   3.758%   $62.6283   $62.63   $62.65   $62.60  
  Purchase #6 $238.69   10.567%   $263.9124   $263.91   $263.90   $263.90  
  Purchase #7 $21.70   5.808%   $22.9603   $22.96   $22.95   $23.00  
  7 purchase totals = $699.96       $763.3073   $763.30   $763.30   $763.30