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 $227.87   12.210%   $255.6929   $255.69   $255.70   $255.70  
  Purchase #2 $208.97   13.618%   $237.4275   $237.43   $237.45   $237.40  
  Purchase #3 $154.34   13.159%   $174.6496   $174.65   $174.65   $174.60  
  Purchase #4 $216.50   7.242%   $232.1789   $232.18   $232.20   $232.20  
  Purchase #5 $205.39   5.401%   $216.4831   $216.48   $216.50   $216.50  
  Purchase #6 $165.50   6.518%   $176.2873   $176.29   $176.30   $176.30  
  Purchase #7 $114.60   9.421%   $125.3965   $125.40   $125.40   $125.40  
  7 purchase totals = $1,293.17       $1,418.1158   $1,418.12   $1,418.20   $1,418.10