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	$211.28	13.834%	$240.5085	$240.51	$240.50	$240.50
Purchase #2	$31.82	5.200%	$33.4746	$33.47	$33.45	$33.50
Purchase #3	$196.44	4.429%	$205.1403	$205.14	$205.15	$205.10
Purchase #4	$12.68	8.607%	$13.7714	$13.77	$13.75	$13.80
Purchase #5	$212.39	7.307%	$227.9093	$227.91	$227.90	$227.90
Purchase #6	$92.61	6.482%	$98.613	$98.61	$98.60	$98.60
Purchase #7	$151.80	13.394%	$172.1321	$172.13	$172.15	$172.10
7 purchase totals =	$909.02		$991.5492	$991.54	$991.50	$991.50