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	$74.81	13.814%	$85.1443	$85.14	$85.15	$85.10
Purchase #2	$243.47	5.314%	$256.408	$256.41	$256.40	$256.40
Purchase #3	$9.72	8.796%	$10.575	$10.58	$10.60	$10.60
Purchase #4	$21.63	7.746%	$23.3055	$23.31	$23.30	$23.30
Purchase #5	$144.87	4.517%	$151.4138	$151.41	$151.40	$151.40
Purchase #6	$127.45	4.171%	$132.7659	$132.77	$132.75	$132.80
Purchase #7	$5.32	12.483%	$5.9841	$5.98	$6.00	$6.00
7 purchase totals =	$627.27		$665.5966	$665.60	$665.60	$665.60