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	$123.39	4.171%	$128.5366	$128.54	$128.55	$128.50
Purchase #2	$123.49	6.627%	$131.6737	$131.67	$131.65	$131.70
Purchase #3	$214.93	10.536%	$237.575	$237.58	$237.60	$237.60
Purchase #4	$30.33	11.790%	$33.9059	$33.91	$33.90	$33.90
Purchase #5	$70.89	9.435%	$77.5785	$77.58	$77.60	$77.60
Purchase #6	$51.28	7.756%	$55.2573	$55.26	$55.25	$55.30
Purchase #7	$15.89	4.613%	$16.623	$16.62	$16.60	$16.60
7 purchase totals =	$630.20		$681.1500	$681.16	$681.15	$681.20