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	$61.84	4.834%	$64.8293	$64.83	$64.85	$64.80
Purchase #2	$53.42	9.652%	$58.5761	$58.58	$58.60	$58.60
Purchase #3	$82.97	9.223%	$90.6223	$90.62	$90.60	$90.60
Purchase #4	$235.45	7.784%	$253.7774	$253.78	$253.80	$253.80
Purchase #5	$20.69	5.468%	$21.8213	$21.82	$21.80	$21.80
Purchase #6	$33.55	12.395%	$37.7085	$37.71	$37.70	$37.70
Purchase #7	$150.95	9.466%	$165.2389	$165.24	$165.25	$165.20
7 purchase totals =	$638.87		$692.5738	$692.58	$692.60	$692.50