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	$250.71	11.244%	$278.8998	$278.90	$278.90	$278.90
Purchase #2	$224.91	13.501%	$255.2751	$255.28	$255.30	$255.30
Purchase #3	$24.30	6.389%	$25.8525	$25.85	$25.85	$25.90
Purchase #4	$234.57	7.249%	$251.574	$251.57	$251.55	$251.60
Purchase #5	$63.62	13.680%	$72.3232	$72.32	$72.30	$72.30
Purchase #6	$41.46	10.224%	$45.6989	$45.70	$45.70	$45.70
Purchase #7	$159.98	4.439%	$167.0815	$167.08	$167.10	$167.10
7 purchase totals =	$999.55		$1,096.7050	$1,096.70	$1,096.70	$1,096.80