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	$126.90	4.745%	$132.9214	$132.92	$132.90	$132.90
Purchase #2	$177.49	6.468%	$188.9701	$188.97	$188.95	$189.00
Purchase #3	$92.85	12.779%	$104.7153	$104.72	$104.70	$104.70
Purchase #4	$11.27	11.339%	$12.5479	$12.55	$12.55	$12.50
Purchase #5	$208.60	7.378%	$223.9905	$223.99	$224.00	$224.00
Purchase #6	$53.43	11.275%	$59.4542	$59.45	$59.45	$59.50
Purchase #7	$161.91	4.335%	$168.9288	$168.93	$168.95	$168.90
7 purchase totals =	$832.45		$891.5282	$891.53	$891.50	$891.50