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 $86.68   13.353%   $98.2544   $98.25   $98.25   $98.30  
  Purchase #2 $176.64   9.548%   $193.5056   $193.51   $193.50   $193.50  
  Purchase #3 $164.44   12.242%   $184.5707   $184.57   $184.55   $184.60  
  Purchase #4 $153.80   10.480%   $169.9182   $169.92   $169.90   $169.90  
  Purchase #5 $245.30   4.577%   $256.5274   $256.53   $256.55   $256.50  
  Purchase #6 $154.65   9.738%   $169.7098   $169.71   $169.70   $169.70  
  Purchase #7 $49.91   12.826%   $56.3115   $56.31   $56.30   $56.30  
  7 purchase totals = $1,031.42       $1,128.7976   $1,128.80   $1,128.75   $1,128.80