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	$14.52	9.346%	$15.877	$15.88	$15.90	$15.90
Purchase #2	$30.69	3.724%	$31.8329	$31.83	$31.85	$31.80
Purchase #3	$181.52	10.277%	$200.1748	$200.17	$200.15	$200.20
Purchase #4	$143.46	4.807%	$150.3561	$150.36	$150.35	$150.40
Purchase #5	$248.91	4.574%	$260.2951	$260.30	$260.30	$260.30
Purchase #6	$35.78	4.856%	$37.5175	$37.52	$37.50	$37.50
Purchase #7	$80.41	5.417%	$84.7658	$84.77	$84.75	$84.80
7 purchase totals =	$735.29		$780.8192	$780.83	$780.80	$780.90