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	$183.56	13.335%	$208.0377	$208.04	$208.05	$208.00
Purchase #2	$248.82	7.220%	$266.7848	$266.78	$266.80	$266.80
Purchase #3	$32.48	3.757%	$33.7003	$33.70	$33.70	$33.70
Purchase #4	$131.73	10.211%	$145.181	$145.18	$145.20	$145.20
Purchase #5	$59.31	5.401%	$62.5133	$62.51	$62.50	$62.50
Purchase #6	$72.52	7.103%	$77.6711	$77.67	$77.65	$77.70
Purchase #7	$164.80	12.197%	$184.9007	$184.90	$184.90	$184.90
7 purchase totals =	$893.22		$978.7889	$978.78	$978.80	$978.80