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 $67.34   13.316%   $76.307   $76.31   $76.30   $76.30  
  Purchase #2 $54.67   7.178%   $58.5942   $58.59   $58.60   $58.60  
  Purchase #3 $241.44   7.448%   $259.4225   $259.42   $259.40   $259.40  
  Purchase #4 $206.48   12.377%   $232.036   $232.04   $232.05   $232.00  
  Purchase #5 $104.87   9.187%   $114.5044   $114.50   $114.50   $114.50  
  Purchase #6 $214.85   13.645%   $244.1663   $244.17   $244.15   $244.20  
  Purchase #7 $181.90   9.624%   $199.4061   $199.41   $199.40   $199.40  
  7 purchase totals = $1,071.55       $1,184.4365   $1,184.44   $1,184.40   $1,184.40