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 $59.93   7.207%   $64.2492   $64.25   $64.25   $64.20  
  Purchase #2 $205.29   13.248%   $232.4868   $232.49   $232.50   $232.50  
  Purchase #3 $65.61   4.379%   $68.4831   $68.48   $68.50   $68.50  
  Purchase #4 $225.87   10.254%   $249.0307   $249.03   $249.05   $249.00  
  Purchase #5 $76.57   5.420%   $80.7201   $80.72   $80.70   $80.70  
  Purchase #6 $125.93   13.118%   $142.4495   $142.45   $142.45   $142.40  
  Purchase #7 $18.63   6.688%   $19.876   $19.88   $19.90   $19.90  
  7 purchase totals = $777.83       $857.2954   $857.30   $857.35   $857.20