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	$52.94	5.834%	$56.0285	$56.03	$56.05	$56.00
Purchase #2	$106.65	9.627%	$116.9172	$116.92	$116.90	$116.90
Purchase #3	$26.47	9.193%	$28.9034	$28.90	$28.90	$28.90
Purchase #4	$37.62	8.675%	$40.8835	$40.88	$40.90	$40.90
Purchase #5	$147.70	11.341%	$164.4507	$164.45	$164.45	$164.50
Purchase #6	$47.42	4.634%	$49.6174	$49.62	$49.60	$49.60
Purchase #7	$104.67	11.127%	$116.3166	$116.32	$116.30	$116.30
7 purchase totals =	$523.47		$573.1173	$573.12	$573.10	$573.10