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	$50.91	10.776%	$56.3961	$56.40	$56.40	$56.40
Purchase #2	$106.83	11.257%	$118.8559	$118.86	$118.85	$118.90
Purchase #3	$123.91	11.599%	$138.2823	$138.28	$138.30	$138.30
Purchase #4	$134.28	8.191%	$145.2789	$145.28	$145.30	$145.30
Purchase #5	$228.76	4.262%	$238.5098	$238.51	$238.50	$238.50
Purchase #6	$64.93	5.449%	$68.468	$68.47	$68.45	$68.50
Purchase #7	$135.89	10.462%	$150.1068	$150.11	$150.10	$150.10
7 purchase totals =	$845.51		$915.8978	$915.91	$915.90	$916.00