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	$124.49	5.521%	$131.3631	$131.36	$131.35	$131.40
Purchase #2	$153.65	5.707%	$162.4188	$162.42	$162.40	$162.40
Purchase #3	$38.83	12.299%	$43.6057	$43.61	$43.60	$43.60
Purchase #4	$55.49	4.680%	$58.0869	$58.09	$58.10	$58.10
Purchase #5	$62.77	6.154%	$66.6329	$66.63	$66.65	$66.60
Purchase #6	$74.26	11.536%	$82.8266	$82.83	$82.85	$82.80
Purchase #7	$238.89	12.382%	$268.4694	$268.47	$268.45	$268.50
7 purchase totals =	$748.38		$813.4034	$813.41	$813.40	$813.40