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	$55.95	6.314%	$59.4827	$59.48	$59.50	$59.50
Purchase #2	$203.86	3.805%	$211.6169	$211.62	$211.60	$211.60
Purchase #3	$124.51	5.328%	$131.1439	$131.14	$131.15	$131.10
Purchase #4	$157.67	13.717%	$179.2976	$179.30	$179.30	$179.30
Purchase #5	$106.91	10.587%	$118.2286	$118.23	$118.25	$118.20
Purchase #6	$149.78	8.393%	$162.351	$162.35	$162.35	$162.40
Purchase #7	$48.91	6.258%	$51.9708	$51.97	$51.95	$52.00
7 purchase totals =	$847.59		$914.0915	$914.09	$914.10	$914.10