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	$36.50	7.856%	$39.3674	$39.37	$39.35	$39.40
Purchase #2	$120.29	3.666%	$124.6998	$124.70	$124.70	$124.70
Purchase #3	$48.84	10.333%	$53.8866	$53.89	$53.90	$53.90
Purchase #4	$99.28	12.676%	$111.8647	$111.86	$111.85	$111.90
Purchase #5	$150.64	11.367%	$167.7632	$167.76	$167.75	$167.80
Purchase #6	$60.70	9.136%	$66.2456	$66.25	$66.25	$66.20
Purchase #7	$16.36	7.748%	$17.6276	$17.63	$17.65	$17.60
7 purchase totals =	$532.61		$581.4549	$581.46	$581.45	$581.50