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	$121.73	12.194%	$136.5738	$136.57	$136.55	$136.60
Purchase #2	$158.72	8.519%	$172.2414	$172.24	$172.25	$172.20
Purchase #3	$18.79	3.615%	$19.4693	$19.47	$19.45	$19.50
Purchase #4	$93.74	7.268%	$100.553	$100.55	$100.55	$100.60
Purchase #5	$96.98	9.181%	$105.8837	$105.88	$105.90	$105.90
Purchase #6	$97.89	7.185%	$104.9234	$104.92	$104.90	$104.90
Purchase #7	$174.26	3.231%	$179.8903	$179.89	$179.90	$179.90
7 purchase totals =	$762.11		$819.5349	$819.52	$819.50	$819.60