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	$25.95	11.519%	$28.9392	$28.94	$28.95	$28.90
Purchase #2	$101.58	11.306%	$113.0646	$113.06	$113.05	$113.10
Purchase #3	$158.72	8.763%	$172.6286	$172.63	$172.65	$172.60
Purchase #4	$16.62	10.525%	$18.3693	$18.37	$18.35	$18.40
Purchase #5	$49.89	7.788%	$53.7754	$53.78	$53.80	$53.80
Purchase #6	$88.71	13.275%	$100.4863	$100.49	$100.50	$100.50
Purchase #7	$72.86	11.841%	$81.4874	$81.49	$81.50	$81.50
7 purchase totals =	$514.33		$568.7508	$568.76	$568.80	$568.80