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 $245.63   8.372%   $266.1941   $266.19   $266.20   $266.20  
  Purchase #2 $62.36   8.250%   $67.5047   $67.50   $67.50   $67.50  
  Purchase #3 $114.65   4.505%   $119.815   $119.82   $119.80   $119.80  
  Purchase #4 $214.66   12.161%   $240.7648   $240.76   $240.75   $240.80  
  Purchase #5 $230.86   8.140%   $249.652   $249.65   $249.65   $249.70  
  Purchase #6 $116.76   11.585%   $130.2866   $130.29   $130.30   $130.30  
  Purchase #7 $235.79   9.103%   $257.254   $257.25   $257.25   $257.30  
  7 purchase totals = $1,220.71       $1,331.4712   $1,331.46   $1,331.45   $1,331.60