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	$138.29	8.377%	$149.8746	$149.87	$149.85	$149.90
Purchase #2	$111.98	13.521%	$127.1208	$127.12	$127.10	$127.10
Purchase #3	$70.95	4.432%	$74.0945	$74.09	$74.10	$74.10
Purchase #4	$39.25	10.425%	$43.3418	$43.34	$43.35	$43.30
Purchase #5	$132.56	11.758%	$148.1464	$148.15	$148.15	$148.10
Purchase #6	$48.29	9.311%	$52.7863	$52.79	$52.80	$52.80
Purchase #7	$105.54	6.760%	$112.6745	$112.67	$112.65	$112.70
7 purchase totals =	$646.86		$708.0389	$708.03	$708.00	$708.00