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 $215.57   12.445%   $242.3977   $242.40   $242.40   $242.40  
  Purchase #2 $209.72   11.556%   $233.9552   $233.96   $233.95   $234.00  
  Purchase #3 $119.90   8.103%   $129.6155   $129.62   $129.60   $129.60  
  Purchase #4 $27.82   4.213%   $28.9921   $28.99   $29.00   $29.00  
  Purchase #5 $73.49   7.451%   $78.9657   $78.97   $78.95   $79.00  
  Purchase #6 $64.88   12.484%   $72.9796   $72.98   $73.00   $73.00  
  Purchase #7 $246.36   13.849%   $280.4784   $280.48   $280.50   $280.50  
  7 purchase totals = $957.74       $1,067.3842   $1,067.40   $1,067.40   $1,067.50