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	$87.75	3.299%	$90.6449	$90.64	$90.65	$90.60
Purchase #2	$184.56	6.670%	$196.8702	$196.87	$196.85	$196.90
Purchase #3	$44.51	4.455%	$46.4929	$46.49	$46.50	$46.50
Purchase #4	$33.95	10.748%	$37.5989	$37.60	$37.60	$37.60
Purchase #5	$32.70	11.620%	$36.4997	$36.50	$36.50	$36.50
Purchase #6	$198.76	13.765%	$226.1193	$226.12	$226.10	$226.10
Purchase #7	$198.68	5.779%	$210.1617	$210.16	$210.15	$210.20
7 purchase totals =	$780.91		$844.3876	$844.38	$844.35	$844.40