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 $57.30   13.852%   $65.2372   $65.24   $65.25   $65.20  
  Purchase #2 $240.67   7.680%   $259.1535   $259.15   $259.15   $259.20  
  Purchase #3 $94.35   12.379%   $106.0296   $106.03   $106.05   $106.00  
  Purchase #4 $84.75   12.115%   $95.0175   $95.02   $95.00   $95.00  
  Purchase #5 $97.69   9.493%   $106.9637   $106.96   $106.95   $107.00  
  Purchase #6 $101.49   4.156%   $105.7079   $105.71   $105.70   $105.70  
  Purchase #7 $81.92   5.577%   $86.4887   $86.49   $86.50   $86.50  
  7 purchase totals = $758.17       $824.5981   $824.60   $824.60   $824.60