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	$220.66	13.618%	$250.7095	$250.71	$250.70	$250.70
Purchase #2	$92.90	6.116%	$98.5818	$98.58	$98.60	$98.60
Purchase #3	$28.95	13.481%	$32.8527	$32.85	$32.85	$32.90
Purchase #4	$77.81	9.341%	$85.0782	$85.08	$85.10	$85.10
Purchase #5	$57.82	10.809%	$64.0698	$64.07	$64.05	$64.10
Purchase #6	$250.82	3.615%	$259.8871	$259.89	$259.90	$259.90
Purchase #7	$45.72	7.694%	$49.2377	$49.24	$49.25	$49.20
7 purchase totals =	$774.68		$840.4168	$840.42	$840.45	$840.50