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 $246.78   7.448%   $265.1602   $265.16   $265.15   $265.20  
  Purchase #2 $164.79   6.794%   $175.9858   $175.99   $176.00   $176.00  
  Purchase #3 $48.81   4.515%   $51.0138   $51.01   $51.00   $51.00  
  Purchase #4 $108.55   7.418%   $116.6022   $116.60   $116.60   $116.60  
  Purchase #5 $138.84   13.271%   $157.2655   $157.27   $157.25   $157.30  
  Purchase #6 $125.38   5.675%   $132.4953   $132.50   $132.50   $132.50  
  Purchase #7 $108.49   11.723%   $121.2083   $121.21   $121.20   $121.20  
  7 purchase totals = $941.64       $1,019.7311   $1,019.74   $1,019.70   $1,019.80