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	$53.31	11.781%	$59.5905	$59.59	$59.60	$59.60
Purchase #2	$220.74	13.490%	$250.5178	$250.52	$250.50	$250.50
Purchase #3	$222.91	3.250%	$230.1546	$230.15	$230.15	$230.20
Purchase #4	$117.76	13.306%	$133.4291	$133.43	$133.45	$133.40
Purchase #5	$94.83	6.183%	$100.6933	$100.69	$100.70	$100.70
Purchase #6	$14.68	3.356%	$15.1727	$15.17	$15.15	$15.20
Purchase #7	$130.50	12.603%	$146.9469	$146.95	$146.95	$146.90
7 purchase totals =	$854.73		$936.5049	$936.50	$936.50	$936.50