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 $216.46   12.820%   $244.2102   $244.21   $244.20   $244.20  
  Purchase #2 $24.28   12.169%   $27.2346   $27.23   $27.25   $27.20  
  Purchase #3 $203.93   10.127%   $224.582   $224.58   $224.60   $224.60  
  Purchase #4 $101.52   13.236%   $114.9572   $114.96   $114.95   $115.00  
  Purchase #5 $104.98   13.590%   $119.2468   $119.25   $119.25   $119.20  
  Purchase #6 $96.66   4.527%   $101.0358   $101.04   $101.05   $101.00  
  Purchase #7 $119.65   11.506%   $133.4169   $133.42   $133.40   $133.40  
  7 purchase totals = $867.48       $964.6835   $964.69   $964.70   $964.60