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	$74.55	5.820%	$78.8888	$78.89	$78.90	$78.90
Purchase #2	$246.92	7.166%	$264.6143	$264.61	$264.60	$264.60
Purchase #3	$32.62	13.670%	$37.0792	$37.08	$37.10	$37.10
Purchase #4	$21.52	4.364%	$22.4591	$22.46	$22.45	$22.50
Purchase #5	$17.46	12.431%	$19.6305	$19.63	$19.65	$19.60
Purchase #6	$18.92	12.523%	$21.2894	$21.29	$21.30	$21.30
Purchase #7	$140.59	13.283%	$159.2646	$159.26	$159.25	$159.30
7 purchase totals =	$552.58		$603.2259	$603.22	$603.25	$603.30