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	$55.76	6.869%	$59.5902	$59.59	$59.60	$59.60
Purchase #2	$24.80	10.748%	$27.4655	$27.47	$27.45	$27.50
Purchase #3	$27.54	4.608%	$28.809	$28.81	$28.80	$28.80
Purchase #4	$188.31	10.172%	$207.4649	$207.46	$207.45	$207.50
Purchase #5	$193.71	11.591%	$216.1629	$216.16	$216.15	$216.20
Purchase #6	$71.96	8.513%	$78.086	$78.09	$78.10	$78.10
Purchase #7	$151.94	13.724%	$172.7922	$172.79	$172.80	$172.80
7 purchase totals =	$714.02		$790.3707	$790.37	$790.35	$790.50