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	$46.60	9.147%	$50.8625	$50.86	$50.85	$50.90
Purchase #2	$22.31	11.613%	$24.9009	$24.90	$24.90	$24.90
Purchase #3	$139.88	4.104%	$145.6207	$145.62	$145.60	$145.60
Purchase #4	$89.37	5.452%	$94.2425	$94.24	$94.25	$94.20
Purchase #5	$39.49	13.627%	$44.8713	$44.87	$44.85	$44.90
Purchase #6	$176.81	7.728%	$190.4739	$190.47	$190.45	$190.50
Purchase #7	$68.66	11.574%	$76.6067	$76.61	$76.60	$76.60
7 purchase totals =	$583.12		$627.5785	$627.57	$627.50	$627.60