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	$88.66	13.353%	$100.4988	$100.50	$100.50	$100.50
Purchase #2	$179.79	4.607%	$188.0729	$188.07	$188.05	$188.10
Purchase #3	$176.77	13.521%	$200.6711	$200.67	$200.65	$200.70
Purchase #4	$183.73	7.327%	$197.1919	$197.19	$197.20	$197.20
Purchase #5	$79.32	11.252%	$88.2451	$88.25	$88.25	$88.20
Purchase #6	$98.55	6.260%	$104.7192	$104.72	$104.70	$104.70
Purchase #7	$35.72	12.261%	$40.0996	$40.10	$40.10	$40.10
7 purchase totals =	$842.54		$919.4986	$919.50	$919.45	$919.50