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 $116.85   3.240%   $120.6359   $120.64   $120.65   $120.60  
  Purchase #2 $250.82   4.438%   $261.9514   $261.95   $261.95   $262.00  
  Purchase #3 $226.35   7.102%   $242.4254   $242.43   $242.45   $242.40  
  Purchase #4 $100.73   11.665%   $112.4802   $112.48   $112.50   $112.50  
  Purchase #5 $154.98   12.209%   $173.9015   $173.90   $173.90   $173.90  
  Purchase #6 $77.36   11.718%   $86.425   $86.43   $86.45   $86.40  
  Purchase #7 $246.80   7.759%   $265.9492   $265.95   $265.95   $265.90  
  7 purchase totals = $1,173.89       $1,263.7686   $1,263.78   $1,263.85   $1,263.70