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 $249.68   11.397%   $278.136   $278.14   $278.15   $278.10  
  Purchase #2 $106.37   9.514%   $116.49   $116.49   $116.50   $116.50  
  Purchase #3 $28.71   13.800%   $32.672   $32.67   $32.65   $32.70  
  Purchase #4 $214.31   9.532%   $234.738   $234.74   $234.75   $234.70  
  Purchase #5 $240.69   12.675%   $271.1975   $271.20   $271.20   $271.20  
  Purchase #6 $164.60   7.691%   $177.2594   $177.26   $177.25   $177.30  
  Purchase #7 $82.75   12.330%   $92.9531   $92.95   $92.95   $93.00  
  7 purchase totals = $1,087.11       $1,203.4460   $1,203.45   $1,203.45   $1,203.50