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 $191.95   8.494%   $208.2542   $208.25   $208.25   $208.30  
  Purchase #2 $58.41   11.797%   $65.3006   $65.30   $65.30   $65.30  
  Purchase #3 $104.79   8.662%   $113.8669   $113.87   $113.85   $113.90  
  Purchase #4 $77.76   5.493%   $82.0314   $82.03   $82.05   $82.00  
  Purchase #5 $232.42   10.261%   $256.2686   $256.27   $256.25   $256.30  
  Purchase #6 $7.70   11.507%   $8.586   $8.59   $8.60   $8.60  
  Purchase #7 $42.91   9.625%   $47.0401   $47.04   $47.05   $47.00  
  7 purchase totals = $715.94       $781.3478   $781.35   $781.35   $781.40