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	$243.62	5.135%	$256.1299	$256.13	$256.15	$256.10
Purchase #2	$141.95	8.225%	$153.6254	$153.63	$153.65	$153.60
Purchase #3	$250.32	10.105%	$275.6148	$275.61	$275.60	$275.60
Purchase #4	$213.96	4.639%	$223.8856	$223.89	$223.90	$223.90
Purchase #5	$101.98	12.546%	$114.7744	$114.77	$114.75	$114.80
Purchase #6	$117.80	12.278%	$132.2635	$132.26	$132.25	$132.30
Purchase #7	$116.85	9.275%	$127.6878	$127.69	$127.70	$127.70
7 purchase totals =	$1,186.48		$1,283.9814	$1,283.98	$1,284.00	$1,284.00