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 $64.77   6.464%   $68.9567   $68.96   $68.95   $69.00  
  Purchase #2 $237.68   9.542%   $260.3594   $260.36   $260.35   $260.40  
  Purchase #3 $71.47   8.147%   $77.2927   $77.29   $77.30   $77.30  
  Purchase #4 $17.37   8.810%   $18.9003   $18.90   $18.90   $18.90  
  Purchase #5 $90.76   5.329%   $95.5966   $95.60   $95.60   $95.60  
  Purchase #6 $74.45   5.858%   $78.8113   $78.81   $78.80   $78.80  
  Purchase #7 $103.43   11.568%   $115.3948   $115.39   $115.40   $115.40  
  7 purchase totals = $659.93       $715.3118   $715.31   $715.30   $715.40