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	$191.83	6.308%	$203.9306	$203.93	$203.95	$203.90
Purchase #2	$7.41	3.269%	$7.6522	$7.65	$7.65	$7.70
Purchase #3	$180.67	5.610%	$190.8056	$190.81	$190.80	$190.80
Purchase #4	$195.93	11.504%	$218.4698	$218.47	$218.45	$218.50
Purchase #5	$136.74	5.863%	$144.7571	$144.76	$144.75	$144.80
Purchase #6	$158.58	10.249%	$174.8329	$174.83	$174.85	$174.80
Purchase #7	$33.87	13.120%	$38.3137	$38.31	$38.30	$38.30
7 purchase totals =	$905.03		$978.7619	$978.76	$978.75	$978.80