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 $175.63   13.534%   $199.3998   $199.40   $199.40   $199.40  
  Purchase #2 $164.47   10.164%   $181.1867   $181.19   $181.20   $181.20  
  Purchase #3 $155.42   9.147%   $169.6363   $169.64   $169.65   $169.60  
  Purchase #4 $21.39   5.593%   $22.5863   $22.59   $22.60   $22.60  
  Purchase #5 $243.58   7.265%   $261.2761   $261.28   $261.30   $261.30  
  Purchase #6 $102.73   6.438%   $109.3438   $109.34   $109.35   $109.30  
  Purchase #7 $214.95   7.388%   $230.8305   $230.83   $230.85   $230.80  
  7 purchase totals = $1,078.17       $1,174.2595   $1,174.27   $1,174.35   $1,174.20