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	$73.87	6.215%	$78.461	$78.46	$78.45	$78.50
Purchase #2	$9.63	4.183%	$10.0328	$10.03	$10.05	$10.00
Purchase #3	$235.27	3.664%	$243.8903	$243.89	$243.90	$243.90
Purchase #4	$145.75	13.773%	$165.8241	$165.82	$165.80	$165.80
Purchase #5	$173.46	4.246%	$180.8251	$180.83	$180.85	$180.80
Purchase #6	$19.35	5.324%	$20.3802	$20.38	$20.40	$20.40
Purchase #7	$13.53	12.365%	$15.203	$15.20	$15.20	$15.20
7 purchase totals =	$670.86		$714.6165	$714.61	$714.65	$714.60