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 $64.39   12.592%   $72.498   $72.50   $72.50   $72.50  
  Purchase #2 $115.95   12.289%   $130.1991   $130.20   $130.20   $130.20  
  Purchase #3 $214.92   6.677%   $229.2702   $229.27   $229.25   $229.30  
  Purchase #4 $11.90   5.627%   $12.5696   $12.57   $12.55   $12.60  
  Purchase #5 $87.71   6.186%   $93.1357   $93.14   $93.15   $93.10  
  Purchase #6 $243.32   13.323%   $275.7375   $275.74   $275.75   $275.70  
  Purchase #7 $217.31   11.447%   $242.1855   $242.19   $242.20   $242.20  
  7 purchase totals = $955.50       $1,055.5956   $1,055.61   $1,055.60   $1,055.60