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	$75.85	5.108%	$79.7244	$79.72	$79.70	$79.70
Purchase #2	$98.71	7.413%	$106.0274	$106.03	$106.05	$106.00
Purchase #3	$73.77	13.207%	$83.5128	$83.51	$83.50	$83.50
Purchase #4	$173.47	8.598%	$188.385	$188.39	$188.40	$188.40
Purchase #5	$17.87	3.578%	$18.5094	$18.51	$18.50	$18.50
Purchase #6	$65.54	9.566%	$71.8096	$71.81	$71.80	$71.80
Purchase #7	$247.85	4.756%	$259.6377	$259.64	$259.65	$259.60
7 purchase totals =	$753.06		$807.6063	$807.61	$807.60	$807.50