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	$129.79	13.283%	$147.03	$147.03	$147.05	$147.00
Purchase #2	$166.37	7.160%	$178.2821	$178.28	$178.30	$178.30
Purchase #3	$74.88	5.174%	$78.7543	$78.75	$78.75	$78.80
Purchase #4	$16.73	12.420%	$18.8079	$18.81	$18.80	$18.80
Purchase #5	$72.92	7.463%	$78.362	$78.36	$78.35	$78.40
Purchase #6	$42.58	9.578%	$46.6583	$46.66	$46.65	$46.70
Purchase #7	$147.25	7.722%	$158.6206	$158.62	$158.60	$158.60
7 purchase totals =	$650.52		$706.5152	$706.51	$706.50	$706.60