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	$148.85	12.346%	$167.227	$167.23	$167.25	$167.20
Purchase #2	$39.92	13.551%	$45.3296	$45.33	$45.35	$45.30
Purchase #3	$155.49	11.171%	$172.8598	$172.86	$172.85	$172.90
Purchase #4	$66.77	3.251%	$68.9407	$68.94	$68.95	$68.90
Purchase #5	$36.47	4.235%	$38.0145	$38.01	$38.00	$38.00
Purchase #6	$91.75	5.547%	$96.8394	$96.84	$96.85	$96.80
Purchase #7	$11.56	10.573%	$12.7822	$12.78	$12.80	$12.80
7 purchase totals =	$550.81		$601.9932	$601.99	$602.05	$601.90