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	$105.61	6.547%	$112.5243	$112.52	$112.50	$112.50
Purchase #2	$179.28	7.324%	$192.4105	$192.41	$192.40	$192.40
Purchase #3	$69.28	4.324%	$72.2757	$72.28	$72.30	$72.30
Purchase #4	$114.85	7.870%	$123.8887	$123.89	$123.90	$123.90
Purchase #5	$175.71	4.515%	$183.6433	$183.64	$183.65	$183.60
Purchase #6	$155.64	6.644%	$165.9807	$165.98	$166.00	$166.00
Purchase #7	$119.82	11.142%	$133.1703	$133.17	$133.15	$133.20
7 purchase totals =	$920.19		$983.8935	$983.89	$983.90	$983.90