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 $60.99   8.232%   $66.0107   $66.01   $66.00   $66.00  
  Purchase #2 $142.96   10.206%   $157.5505   $157.55   $157.55   $157.60  
  Purchase #3 $109.57   3.167%   $113.0401   $113.04   $113.05   $113.00  
  Purchase #4 $213.28   13.731%   $242.5655   $242.57   $242.55   $242.60  
  Purchase #5 $199.73   9.149%   $218.0033   $218.00   $218.00   $218.00  
  Purchase #6 $22.38   13.723%   $25.4512   $25.45   $25.45   $25.50  
  Purchase #7 $8.41   5.709%   $8.8901   $8.89   $8.90   $8.90  
  7 purchase totals = $757.32       $831.5114   $831.51   $831.50   $831.60