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 $70.27   5.776%   $74.3288   $74.33   $74.35   $74.30  
  Purchase #2 $90.61   5.485%   $95.58   $95.58   $95.60   $95.60  
  Purchase #3 $175.34   13.331%   $198.7146   $198.71   $198.70   $198.70  
  Purchase #4 $199.27   8.212%   $215.6341   $215.63   $215.65   $215.60  
  Purchase #5 $44.31   12.858%   $50.0074   $50.01   $50.00   $50.00  
  Purchase #6 $237.75   12.161%   $266.6628   $266.66   $266.65   $266.70  
  Purchase #7 $107.36   6.768%   $114.6261   $114.63   $114.65   $114.60  
  7 purchase totals = $924.91       $1,015.5538   $1,015.55   $1,015.60   $1,015.50