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	$20.25	4.501%	$21.1615	$21.16	$21.15	$21.20
Purchase #2	$18.66	10.530%	$20.6249	$20.62	$20.60	$20.60
Purchase #3	$59.33	12.843%	$66.9498	$66.95	$66.95	$66.90
Purchase #4	$94.77	7.587%	$101.9602	$101.96	$101.95	$102.00
Purchase #5	$201.56	13.291%	$228.3493	$228.35	$228.35	$228.30
Purchase #6	$55.26	10.552%	$61.091	$61.09	$61.10	$61.10
Purchase #7	$173.82	6.794%	$185.6293	$185.63	$185.65	$185.60
7 purchase totals =	$623.65		$685.7660	$685.76	$685.75	$685.70