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	$128.38	13.595%	$145.8333	$145.83	$145.85	$145.80
Purchase #2	$157.57	5.543%	$166.3041	$166.30	$166.30	$166.30
Purchase #3	$18.42	12.568%	$20.735	$20.74	$20.75	$20.70
Purchase #4	$47.65	9.825%	$52.3316	$52.33	$52.35	$52.30
Purchase #5	$156.55	13.461%	$177.6232	$177.62	$177.60	$177.60
Purchase #6	$196.70	6.566%	$209.6153	$209.62	$209.60	$209.60
Purchase #7	$117.34	8.842%	$127.7152	$127.72	$127.70	$127.70
7 purchase totals =	$822.61		$900.1577	$900.16	$900.15	$900.00