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	$32.89	13.629%	$37.3726	$37.37	$37.35	$37.40
Purchase #2	$22.77	10.139%	$25.0787	$25.08	$25.10	$25.10
Purchase #3	$144.49	11.303%	$160.8217	$160.82	$160.80	$160.80
Purchase #4	$74.32	11.617%	$82.9538	$82.95	$82.95	$83.00
Purchase #5	$143.72	6.537%	$153.115	$153.12	$153.10	$153.10
Purchase #6	$54.61	3.796%	$56.683	$56.68	$56.70	$56.70
Purchase #7	$211.65	6.690%	$225.8094	$225.81	$225.80	$225.80
7 purchase totals =	$684.45		$741.8342	$741.83	$741.80	$741.90