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 $65.86   11.296%   $73.2995   $73.30   $73.30   $73.30  
  Purchase #2 $51.87   13.209%   $58.7215   $58.72   $58.70   $58.70  
  Purchase #3 $65.60   11.501%   $73.1447   $73.14   $73.15   $73.10  
  Purchase #4 $191.42   8.499%   $207.6888   $207.69   $207.70   $207.70  
  Purchase #5 $157.55   3.225%   $162.631   $162.63   $162.65   $162.60  
  Purchase #6 $58.79   10.161%   $64.7637   $64.76   $64.75   $64.80  
  Purchase #7 $127.27   3.315%   $131.489   $131.49   $131.50   $131.50  
  7 purchase totals = $718.36       $771.7382   $771.73   $771.75   $771.70