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 $218.26   11.143%   $242.5807   $242.58   $242.60   $242.60  
  Purchase #2 $239.40   6.674%   $255.3776   $255.38   $255.40   $255.40  
  Purchase #3 $84.97   10.525%   $93.9131   $93.91   $93.90   $93.90  
  Purchase #4 $113.68   10.210%   $125.2867   $125.29   $125.30   $125.30  
  Purchase #5 $61.46   9.127%   $67.0695   $67.07   $67.05   $67.10  
  Purchase #6 $221.64   12.509%   $249.3649   $249.36   $249.35   $249.40  
  Purchase #7 $136.70   4.251%   $142.5111   $142.51   $142.50   $142.50  
  7 purchase totals = $1,076.11       $1,176.1036   $1,176.10   $1,176.10   $1,176.20