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 $152.34   8.238%   $164.8898   $164.89   $164.90   $164.90  
  Purchase #2 $233.37   5.138%   $245.3606   $245.36   $245.35   $245.40  
  Purchase #3 $23.98   6.467%   $25.5308   $25.53   $25.55   $25.50  
  Purchase #4 $242.45   13.584%   $275.3844   $275.38   $275.40   $275.40  
  Purchase #5 $239.56   9.549%   $262.4356   $262.44   $262.45   $262.40  
  Purchase #6 $93.53   13.863%   $106.4961   $106.50   $106.50   $106.50  
  Purchase #7 $176.47   9.511%   $193.2541   $193.25   $193.25   $193.30  
  7 purchase totals = $1,161.70       $1,273.3514   $1,273.35   $1,273.40   $1,273.40