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	$28.89	3.251%	$29.8292	$29.83	$29.85	$29.80
Purchase #2	$230.86	12.280%	$259.2096	$259.21	$259.20	$259.20
Purchase #3	$139.71	4.522%	$146.0277	$146.03	$146.05	$146.00
Purchase #4	$153.89	7.613%	$165.6056	$165.61	$165.60	$165.60
Purchase #5	$37.60	10.524%	$41.557	$41.56	$41.55	$41.60
Purchase #6	$151.64	5.598%	$160.1288	$160.13	$160.15	$160.10
Purchase #7	$140.83	5.843%	$149.0587	$149.06	$149.05	$149.10
7 purchase totals =	$883.42		$951.4166	$951.43	$951.45	$951.40