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	$90.46	4.818%	$94.8184	$94.82	$94.80	$94.80
Purchase #2	$26.43	11.495%	$29.4681	$29.47	$29.45	$29.50
Purchase #3	$17.54	13.378%	$19.8865	$19.89	$19.90	$19.90
Purchase #4	$136.46	12.773%	$153.89	$153.89	$153.90	$153.90
Purchase #5	$132.58	9.184%	$144.7561	$144.76	$144.75	$144.80
Purchase #6	$93.63	7.199%	$100.3704	$100.37	$100.35	$100.40
Purchase #7	$11.73	6.855%	$12.5341	$12.53	$12.55	$12.50
7 purchase totals =	$508.83		$555.7236	$555.73	$555.70	$555.80