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	$173.54	6.872%	$185.4657	$185.47	$185.45	$185.50
Purchase #2	$204.27	13.162%	$231.156	$231.16	$231.15	$231.20
Purchase #3	$169.72	4.501%	$177.3591	$177.36	$177.35	$177.40
Purchase #4	$239.52	13.117%	$270.9378	$270.94	$270.95	$270.90
Purchase #5	$16.41	7.184%	$17.5889	$17.59	$17.60	$17.60
Purchase #6	$14.29	3.740%	$14.8244	$14.82	$14.80	$14.80
Purchase #7	$28.84	9.330%	$31.5308	$31.53	$31.55	$31.50
7 purchase totals =	$846.59		$928.8627	$928.87	$928.85	$928.90