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 $246.32   7.161%   $263.959   $263.96   $263.95   $264.00  
  Purchase #2 $70.38   7.825%   $75.8872   $75.89   $75.90   $75.90  
  Purchase #3 $58.40   9.438%   $63.9118   $63.91   $63.90   $63.90  
  Purchase #4 $237.32   10.782%   $262.9078   $262.91   $262.90   $262.90  
  Purchase #5 $118.27   6.418%   $125.8606   $125.86   $125.85   $125.90  
  Purchase #6 $31.99   8.577%   $34.7338   $34.73   $34.75   $34.70  
  Purchase #7 $49.45   11.598%   $55.1852   $55.19   $55.20   $55.20  
  7 purchase totals = $812.13       $882.4454   $882.45   $882.45   $882.50