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	$37.73	13.578%	$42.853	$42.85	$42.85	$42.90
Purchase #2	$158.92	8.708%	$172.7588	$172.76	$172.75	$172.80
Purchase #3	$42.97	12.509%	$48.3451	$48.35	$48.35	$48.30
Purchase #4	$30.54	11.169%	$33.951	$33.95	$33.95	$34.00
Purchase #5	$166.32	4.587%	$173.9491	$173.95	$173.95	$173.90
Purchase #6	$181.70	10.604%	$200.9675	$200.97	$200.95	$201.00
Purchase #7	$12.56	9.552%	$13.7597	$13.76	$13.75	$13.80
7 purchase totals =	$630.74		$686.5842	$686.59	$686.55	$686.70