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 $114.72   10.573%   $126.8493   $126.85   $126.85   $126.80  
  Purchase #2 $106.41   11.386%   $118.5258   $118.53   $118.55   $118.50  
  Purchase #3 $234.91   9.504%   $257.2358   $257.24   $257.25   $257.20  
  Purchase #4 $61.85   12.357%   $69.4928   $69.49   $69.50   $69.50  
  Purchase #5 $139.38   5.834%   $147.5114   $147.51   $147.50   $147.50  
  Purchase #6 $221.47   12.706%   $249.61   $249.61   $249.60   $249.60  
  Purchase #7 $94.55   6.509%   $100.7043   $100.70   $100.70   $100.70  
  7 purchase totals = $973.29       $1,069.9294   $1,069.93   $1,069.95   $1,069.80