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	$134.69	8.408%	$146.0147	$146.01	$146.00	$146.00
Purchase #2	$219.36	5.572%	$231.5827	$231.58	$231.60	$231.60
Purchase #3	$246.89	3.860%	$256.42	$256.42	$256.40	$256.40
Purchase #4	$151.54	7.149%	$162.3736	$162.37	$162.35	$162.40
Purchase #5	$241.74	8.470%	$262.2154	$262.22	$262.20	$262.20
Purchase #6	$21.30	13.398%	$24.1538	$24.15	$24.15	$24.20
Purchase #7	$61.95	8.710%	$67.3458	$67.35	$67.35	$67.30
7 purchase totals =	$1,077.47		$1,150.1060	$1,150.10	$1,150.05	$1,150.10