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	$190.94	13.249%	$216.2376	$216.24	$216.25	$216.20
Purchase #2	$86.63	4.271%	$90.33	$90.33	$90.35	$90.30
Purchase #3	$78.42	3.170%	$80.9059	$80.91	$80.90	$80.90
Purchase #4	$23.89	6.713%	$25.4937	$25.49	$25.50	$25.50
Purchase #5	$111.30	6.278%	$118.2874	$118.29	$118.30	$118.30
Purchase #6	$67.49	8.248%	$73.0566	$73.06	$73.05	$73.10
Purchase #7	$32.84	7.585%	$35.3309	$35.33	$35.35	$35.30
7 purchase totals =	$591.51		$639.6421	$639.65	$639.70	$639.60