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	$10.53	3.293%	$10.8768	$10.88	$10.90	$10.90
Purchase #2	$21.95	10.739%	$24.3072	$24.31	$24.30	$24.30
Purchase #3	$164.54	4.542%	$172.0134	$172.01	$172.00	$172.00
Purchase #4	$158.25	9.607%	$173.4531	$173.45	$173.45	$173.50
Purchase #5	$86.74	3.624%	$89.8835	$89.88	$89.90	$89.90
Purchase #6	$75.40	8.135%	$81.5338	$81.53	$81.55	$81.50
Purchase #7	$156.68	10.602%	$173.2912	$173.29	$173.30	$173.30
7 purchase totals =	$674.09		$725.3590	$725.35	$725.40	$725.40