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 $224.39   7.741%   $241.76   $241.76   $241.75   $241.80  
  Purchase #2 $19.85   7.383%   $21.3155   $21.32   $21.30   $21.30  
  Purchase #3 $29.26   6.817%   $31.2547   $31.25   $31.25   $31.30  
  Purchase #4 $154.55   7.379%   $165.9542   $165.95   $165.95   $166.00  
  Purchase #5 $205.50   5.720%   $217.2546   $217.25   $217.25   $217.30  
  Purchase #6 $182.92   8.228%   $197.9707   $197.97   $197.95   $198.00  
  Purchase #7 $207.87   9.571%   $227.7652   $227.77   $227.75   $227.80  
  7 purchase totals = $1,024.34       $1,103.2749   $1,103.27   $1,103.20   $1,103.50