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	$74.83	11.598%	$83.5088	$83.51	$83.50	$83.50
Purchase #2	$130.65	4.482%	$136.5057	$136.51	$136.50	$136.50
Purchase #3	$110.68	11.567%	$123.4824	$123.48	$123.50	$123.50
Purchase #4	$19.49	6.445%	$20.7461	$20.75	$20.75	$20.70
Purchase #5	$138.88	11.792%	$155.2567	$155.26	$155.25	$155.30
Purchase #6	$244.27	7.724%	$263.1374	$263.14	$263.15	$263.10
Purchase #7	$238.52	9.103%	$260.2325	$260.23	$260.25	$260.20
7 purchase totals =	$957.32		$1,042.8696	$1,042.88	$1,042.90	$1,042.80