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 $158.27   11.242%   $176.0627   $176.06   $176.05   $176.10  
  Purchase #2 $115.50   12.587%   $130.038   $130.04   $130.05   $130.00  
  Purchase #3 $123.84   7.857%   $133.5701   $133.57   $133.55   $133.60  
  Purchase #4 $226.45   11.509%   $252.5121   $252.51   $252.50   $252.50  
  Purchase #5 $193.38   13.493%   $219.4728   $219.47   $219.45   $219.50  
  Purchase #6 $86.27   3.558%   $89.3395   $89.34   $89.35   $89.30  
  Purchase #7 $82.74   11.612%   $92.3478   $92.35   $92.35   $92.30  
  7 purchase totals = $986.45       $1,093.3430   $1,093.34   $1,093.30   $1,093.30