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	$167.43	3.237%	$172.8497	$172.85	$172.85	$172.80
Purchase #2	$176.34	6.207%	$187.2854	$187.29	$187.30	$187.30
Purchase #3	$119.77	6.157%	$127.1442	$127.14	$127.15	$127.10
Purchase #4	$117.49	12.787%	$132.5134	$132.51	$132.50	$132.50
Purchase #5	$73.68	13.233%	$83.4301	$83.43	$83.45	$83.40
Purchase #6	$91.63	8.600%	$99.5102	$99.51	$99.50	$99.50
Purchase #7	$45.67	7.446%	$49.0706	$49.07	$49.05	$49.10
7 purchase totals =	$792.01		$851.8036	$851.80	$851.80	$851.70