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	$36.87	10.168%	$40.6189	$40.62	$40.60	$40.60
Purchase #2	$48.42	6.410%	$51.5237	$51.52	$51.50	$51.50
Purchase #3	$165.57	11.699%	$184.94	$184.94	$184.95	$184.90
Purchase #4	$9.52	5.874%	$10.0792	$10.08	$10.10	$10.10
Purchase #5	$56.34	7.246%	$60.4224	$60.42	$60.40	$60.40
Purchase #6	$178.80	3.248%	$184.6074	$184.61	$184.60	$184.60
Purchase #7	$119.27	7.144%	$127.7906	$127.79	$127.80	$127.80
7 purchase totals =	$614.79		$659.9822	$659.98	$659.95	$659.90