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 $62.74   10.796%   $69.5134   $69.51   $69.50   $69.50  
  Purchase #2 $170.46   12.354%   $191.5186   $191.52   $191.50   $191.50  
  Purchase #3 $11.70   5.838%   $12.383   $12.38   $12.40   $12.40  
  Purchase #4 $166.88   9.681%   $183.0357   $183.04   $183.05   $183.00  
  Purchase #5 $228.88   9.754%   $251.205   $251.21   $251.20   $251.20  
  Purchase #6 $46.89   6.166%   $49.7812   $49.78   $49.80   $49.80  
  Purchase #7 $10.39   6.511%   $11.0665   $11.07   $11.05   $11.10  
  7 purchase totals = $697.94       $768.5034   $768.51   $768.50   $768.50