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	$53.95	10.290%	$59.5015	$59.50	$59.50	$59.50
Purchase #2	$11.91	8.504%	$12.9228	$12.92	$12.90	$12.90
Purchase #3	$191.59	4.275%	$199.7805	$199.78	$199.80	$199.80
Purchase #4	$83.44	5.635%	$88.1418	$88.14	$88.15	$88.10
Purchase #5	$133.52	8.287%	$144.5848	$144.58	$144.60	$144.60
Purchase #6	$240.28	11.839%	$268.7267	$268.73	$268.75	$268.70
Purchase #7	$205.60	5.384%	$216.6695	$216.67	$216.65	$216.70
7 purchase totals =	$920.29		$990.3276	$990.32	$990.35	$990.30