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 $102.42   9.735%   $112.3906   $112.39   $112.40   $112.40  
  Purchase #2 $128.51   9.255%   $140.4036   $140.40   $140.40   $140.40  
  Purchase #3 $183.31   7.590%   $197.2232   $197.22   $197.20   $197.20  
  Purchase #4 $151.99   10.614%   $168.1222   $168.12   $168.10   $168.10  
  Purchase #5 $239.78   3.796%   $248.882   $248.88   $248.90   $248.90  
  Purchase #6 $236.91   6.443%   $252.1741   $252.17   $252.15   $252.20  
  Purchase #7 $157.41   7.110%   $168.6019   $168.60   $168.60   $168.60  
  7 purchase totals = $1,200.33       $1,287.7976   $1,287.78   $1,287.75   $1,287.80