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	$151.82	4.142%	$158.1084	$158.11	$158.10	$158.10
Purchase #2	$92.25	7.521%	$99.1881	$99.19	$99.20	$99.20
Purchase #3	$145.45	13.353%	$164.8719	$164.87	$164.85	$164.90
Purchase #4	$139.45	13.750%	$158.6244	$158.62	$158.60	$158.60
Purchase #5	$245.28	13.300%	$277.9022	$277.90	$277.90	$277.90
Purchase #6	$232.35	13.783%	$264.3748	$264.37	$264.35	$264.40
Purchase #7	$131.30	13.305%	$148.7695	$148.77	$148.75	$148.80
7 purchase totals =	$1,137.90		$1,271.8393	$1,271.83	$1,271.75	$1,271.90