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	$19.61	6.677%	$20.9194	$20.92	$20.90	$20.90
Purchase #2	$140.66	12.610%	$158.3972	$158.40	$158.40	$158.40
Purchase #3	$66.62	6.398%	$70.8823	$70.88	$70.90	$70.90
Purchase #4	$38.32	13.605%	$43.5334	$43.53	$43.55	$43.50
Purchase #5	$58.41	9.836%	$64.1552	$64.16	$64.15	$64.20
Purchase #6	$241.27	8.801%	$262.5042	$262.50	$262.50	$262.50
Purchase #7	$198.53	13.784%	$225.8954	$225.90	$225.90	$225.90
7 purchase totals =	$763.42		$846.2871	$846.29	$846.30	$846.30