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	$9.77	6.636%	$10.4183	$10.42	$10.40	$10.40
Purchase #2	$136.45	11.786%	$152.532	$152.53	$152.55	$152.50
Purchase #3	$218.68	5.356%	$230.3925	$230.39	$230.40	$230.40
Purchase #4	$28.83	3.447%	$29.8238	$29.82	$29.80	$29.80
Purchase #5	$96.42	9.509%	$105.5886	$105.59	$105.60	$105.60
Purchase #6	$165.92	3.550%	$171.8102	$171.81	$171.80	$171.80
Purchase #7	$14.73	7.371%	$15.8157	$15.82	$15.80	$15.80
7 purchase totals =	$670.80		$716.3811	$716.38	$716.35	$716.30