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 $143.84   7.303%   $154.3446   $154.34   $154.35   $154.30  
  Purchase #2 $214.81   13.719%   $244.2798   $244.28   $244.30   $244.30  
  Purchase #3 $175.29   11.494%   $195.4378   $195.44   $195.45   $195.40  
  Purchase #4 $176.76   6.628%   $188.4757   $188.48   $188.50   $188.50  
  Purchase #5 $228.30   8.423%   $247.5297   $247.53   $247.55   $247.50  
  Purchase #6 $57.78   5.603%   $61.0174   $61.02   $61.00   $61.00  
  Purchase #7 $161.94   12.753%   $182.5922   $182.59   $182.60   $182.60  
  7 purchase totals = $1,158.72       $1,273.6772   $1,273.68   $1,273.75   $1,273.60