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	$216.40	11.491%	$241.2665	$241.27	$241.25	$241.30
Purchase #2	$100.84	13.698%	$114.6531	$114.65	$114.65	$114.70
Purchase #3	$198.56	5.244%	$208.9725	$208.97	$208.95	$209.00
Purchase #4	$98.51	13.224%	$111.537	$111.54	$111.55	$111.50
Purchase #5	$56.45	10.479%	$62.3654	$62.37	$62.35	$62.40
Purchase #6	$36.31	9.518%	$39.766	$39.77	$39.75	$39.80
Purchase #7	$18.57	9.332%	$20.303	$20.30	$20.30	$20.30
7 purchase totals =	$725.64		$798.8635	$798.87	$798.80	$799.00