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	$137.39	7.602%	$147.8344	$147.83	$147.85	$147.80
Purchase #2	$147.88	13.417%	$167.7211	$167.72	$167.70	$167.70
Purchase #3	$52.54	10.388%	$57.9979	$58.00	$58.00	$58.00
Purchase #4	$143.89	4.772%	$150.7564	$150.76	$150.75	$150.80
Purchase #5	$47.43	4.233%	$49.4377	$49.44	$49.45	$49.40
Purchase #6	$93.81	11.374%	$104.4799	$104.48	$104.50	$104.50
Purchase #7	$150.98	9.689%	$165.6085	$165.61	$165.60	$165.60
7 purchase totals =	$773.92		$843.8359	$843.84	$843.85	$843.80