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 $237.38   11.314%   $264.2372   $264.24   $264.25   $264.20  
  Purchase #2 $195.74   5.395%   $206.3002   $206.30   $206.30   $206.30  
  Purchase #3 $84.42   8.468%   $91.5687   $91.57   $91.55   $91.60  
  Purchase #4 $249.38   10.401%   $275.318   $275.32   $275.30   $275.30  
  Purchase #5 $153.55   6.749%   $163.9131   $163.91   $163.90   $163.90  
  Purchase #6 $154.83   10.123%   $170.5034   $170.50   $170.50   $170.50  
  Purchase #7 $162.33   6.531%   $172.9318   $172.93   $172.95   $172.90  
  7 purchase totals = $1,237.63       $1,344.7724   $1,344.77   $1,344.75   $1,344.70