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	$56.83	13.353%	$64.4185	$64.42	$64.40	$64.40
Purchase #2	$167.98	6.170%	$178.3444	$178.34	$178.35	$178.30
Purchase #3	$158.33	4.658%	$165.705	$165.71	$165.70	$165.70
Purchase #4	$105.62	5.307%	$111.2253	$111.23	$111.25	$111.20
Purchase #5	$61.85	6.203%	$65.6866	$65.69	$65.70	$65.70
Purchase #6	$79.69	11.190%	$88.6073	$88.61	$88.60	$88.60
Purchase #7	$217.28	4.609%	$227.2944	$227.29	$227.30	$227.30
7 purchase totals =	$847.58		$901.2815	$901.29	$901.30	$901.20