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	$28.76	10.491%	$31.7772	$31.78	$31.80	$31.80
Purchase #2	$136.56	5.680%	$144.3166	$144.32	$144.30	$144.30
Purchase #3	$70.90	8.152%	$76.6798	$76.68	$76.70	$76.70
Purchase #4	$54.58	8.319%	$59.1205	$59.12	$59.10	$59.10
Purchase #5	$6.35	11.239%	$7.0637	$7.06	$7.05	$7.10
Purchase #6	$115.85	6.442%	$123.3131	$123.31	$123.30	$123.30
Purchase #7	$98.33	5.130%	$103.3743	$103.37	$103.35	$103.40
7 purchase totals =	$511.33		$545.6452	$545.64	$545.60	$545.70