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	$243.87	8.535%	$264.6843	$264.68	$264.70	$264.70
Purchase #2	$59.52	13.504%	$67.5576	$67.56	$67.55	$67.60
Purchase #3	$11.29	10.361%	$12.4598	$12.46	$12.45	$12.50
Purchase #4	$39.43	11.209%	$43.8497	$43.85	$43.85	$43.80
Purchase #5	$94.78	5.356%	$99.8564	$99.86	$99.85	$99.90
Purchase #6	$86.28	5.852%	$91.3291	$91.33	$91.35	$91.30
Purchase #7	$107.57	3.826%	$111.6856	$111.69	$111.70	$111.70
7 purchase totals =	$642.74		$691.4225	$691.43	$691.45	$691.50