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	$96.53	3.804%	$100.202	$100.20	$100.20	$100.20
Purchase #2	$102.83	7.251%	$110.2862	$110.29	$110.30	$110.30
Purchase #3	$210.59	13.736%	$239.5166	$239.52	$239.50	$239.50
Purchase #4	$223.60	12.314%	$251.1341	$251.13	$251.15	$251.10
Purchase #5	$153.80	10.714%	$170.2781	$170.28	$170.30	$170.30
Purchase #6	$10.85	6.716%	$11.5787	$11.58	$11.60	$11.60
Purchase #7	$55.65	6.524%	$59.2806	$59.28	$59.30	$59.30
7 purchase totals =	$853.85		$942.2763	$942.28	$942.35	$942.30