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	$159.32	3.303%	$164.5823	$164.58	$164.60	$164.60
Purchase #2	$74.30	12.168%	$83.3408	$83.34	$83.35	$83.30
Purchase #3	$127.75	3.636%	$132.395	$132.40	$132.40	$132.40
Purchase #4	$171.52	12.812%	$193.4951	$193.50	$193.50	$193.50
Purchase #5	$107.79	8.663%	$117.1278	$117.13	$117.15	$117.10
Purchase #6	$88.41	12.869%	$99.7875	$99.79	$99.80	$99.80
Purchase #7	$120.65	5.834%	$127.6887	$127.69	$127.70	$127.70
7 purchase totals =	$849.74		$918.4172	$918.43	$918.50	$918.40