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 $178.78   8.570%   $194.1014   $194.10   $194.10   $194.10  
  Purchase #2 $112.29   11.672%   $125.3965   $125.40   $125.40   $125.40  
  Purchase #3 $66.39   5.681%   $70.1616   $70.16   $70.15   $70.20  
  Purchase #4 $241.66   3.284%   $249.5961   $249.60   $249.60   $249.60  
  Purchase #5 $224.94   13.587%   $255.5026   $255.50   $255.50   $255.50  
  Purchase #6 $214.64   4.432%   $224.1528   $224.15   $224.15   $224.20  
  Purchase #7 $218.33   13.770%   $248.394   $248.39   $248.40   $248.40  
  7 purchase totals = $1,257.03       $1,367.3050   $1,367.30   $1,367.30   $1,367.40