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	$128.87	12.130%	$144.5019	$144.50	$144.50	$144.50
Purchase #2	$127.92	6.821%	$136.6454	$136.65	$136.65	$136.60
Purchase #3	$175.51	7.665%	$188.9628	$188.96	$188.95	$189.00
Purchase #4	$130.91	8.323%	$141.8056	$141.81	$141.80	$141.80
Purchase #5	$177.40	6.312%	$188.5975	$188.60	$188.60	$188.60
Purchase #6	$171.62	7.685%	$184.809	$184.81	$184.80	$184.80
Purchase #7	$77.81	5.196%	$81.853	$81.85	$81.85	$81.90
7 purchase totals =	$990.04		$1,067.1752	$1,067.18	$1,067.15	$1,067.20