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	$188.38	5.569%	$198.8709	$198.87	$198.85	$198.90
Purchase #2	$209.41	11.585%	$233.6701	$233.67	$233.65	$233.70
Purchase #3	$149.39	11.103%	$165.9768	$165.98	$166.00	$166.00
Purchase #4	$7.45	3.289%	$7.695	$7.70	$7.70	$7.70
Purchase #5	$233.59	11.172%	$259.6867	$259.69	$259.70	$259.70
Purchase #6	$106.50	4.292%	$111.071	$111.07	$111.05	$111.10
Purchase #7	$21.75	7.813%	$23.4493	$23.45	$23.45	$23.40
7 purchase totals =	$916.47		$1,000.4198	$1,000.43	$1,000.40	$1,000.50