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	$234.46	11.812%	$262.1544	$262.15	$262.15	$262.20
Purchase #2	$84.61	11.612%	$94.4349	$94.43	$94.45	$94.40
Purchase #3	$115.89	13.141%	$131.1191	$131.12	$131.10	$131.10
Purchase #4	$10.92	3.802%	$11.3352	$11.34	$11.35	$11.30
Purchase #5	$33.42	12.184%	$37.4919	$37.49	$37.50	$37.50
Purchase #6	$95.41	6.163%	$101.2901	$101.29	$101.30	$101.30
Purchase #7	$44.28	5.268%	$46.6127	$46.61	$46.60	$46.60
7 purchase totals =	$618.99		$684.4383	$684.43	$684.45	$684.40