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	$56.30	6.460%	$59.937	$59.94	$59.95	$59.90
Purchase #2	$249.47	4.838%	$261.5394	$261.54	$261.55	$261.50
Purchase #3	$179.76	13.627%	$204.2559	$204.26	$204.25	$204.30
Purchase #4	$154.36	7.163%	$165.4168	$165.42	$165.40	$165.40
Purchase #5	$42.45	4.124%	$44.2006	$44.20	$44.20	$44.20
Purchase #6	$68.78	13.566%	$78.1107	$78.11	$78.10	$78.10
Purchase #7	$21.71	6.692%	$23.1628	$23.16	$23.15	$23.20
7 purchase totals =	$772.83		$836.6232	$836.63	$836.60	$836.60