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 $244.93   11.144%   $272.225   $272.23   $272.25   $272.20  
  Purchase #2 $180.75   8.207%   $195.5842   $195.58   $195.60   $195.60  
  Purchase #3 $40.33   5.567%   $42.5752   $42.58   $42.60   $42.60  
  Purchase #4 $102.73   11.311%   $114.3498   $114.35   $114.35   $114.30  
  Purchase #5 $133.33   7.698%   $143.5937   $143.59   $143.60   $143.60  
  Purchase #6 $34.76   5.394%   $36.635   $36.64   $36.65   $36.60  
  Purchase #7 $146.69   6.258%   $155.8699   $155.87   $155.85   $155.90  
  7 purchase totals = $883.52       $960.8328   $960.84   $960.90   $960.80