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	$244.77	13.816%	$278.5874	$278.59	$278.60	$278.60
Purchase #2	$28.68	8.106%	$31.0048	$31.00	$31.00	$31.00
Purchase #3	$122.27	9.157%	$133.4663	$133.47	$133.45	$133.50
Purchase #4	$198.72	10.499%	$219.5836	$219.58	$219.60	$219.60
Purchase #5	$220.77	13.585%	$250.7616	$250.76	$250.75	$250.80
Purchase #6	$48.77	13.604%	$55.4047	$55.40	$55.40	$55.40
Purchase #7	$76.91	7.716%	$82.8444	$82.84	$82.85	$82.80
7 purchase totals =	$940.89		$1,051.6528	$1,051.64	$1,051.65	$1,051.70