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 $215.68   3.244%   $222.6767   $222.68   $222.70   $222.70  
  Purchase #2 $112.33   6.247%   $119.3473   $119.35   $119.35   $119.30  
  Purchase #3 $177.72   5.207%   $186.9739   $186.97   $186.95   $187.00  
  Purchase #4 $66.79   6.866%   $71.3758   $71.38   $71.40   $71.40  
  Purchase #5 $239.98   5.675%   $253.5989   $253.60   $253.60   $253.60  
  Purchase #6 $149.49   8.307%   $161.9081   $161.91   $161.90   $161.90  
  Purchase #7 $224.66   6.748%   $239.8201   $239.82   $239.80   $239.80  
  7 purchase totals = $1,186.65       $1,255.7008   $1,255.71   $1,255.70   $1,255.70