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	$19.67	11.561%	$21.944	$21.94	$21.95	$21.90
Purchase #2	$30.74	9.843%	$33.7657	$33.77	$33.75	$33.80
Purchase #3	$153.51	12.490%	$172.6834	$172.68	$172.70	$172.70
Purchase #4	$39.87	6.651%	$42.5218	$42.52	$42.50	$42.50
Purchase #5	$207.70	11.516%	$231.6187	$231.62	$231.60	$231.60
Purchase #6	$98.72	5.765%	$104.4112	$104.41	$104.40	$104.40
Purchase #7	$164.82	13.554%	$187.1597	$187.16	$187.15	$187.20
7 purchase totals =	$715.03		$794.1045	$794.10	$794.05	$794.10