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	$15.89	6.858%	$16.9797	$16.98	$17.00	$17.00
Purchase #2	$45.59	10.154%	$50.2192	$50.22	$50.20	$50.20
Purchase #3	$155.65	4.627%	$162.8519	$162.85	$162.85	$162.90
Purchase #4	$19.77	7.679%	$21.2881	$21.29	$21.30	$21.30
Purchase #5	$153.94	8.763%	$167.4298	$167.43	$167.45	$167.40
Purchase #6	$57.47	13.387%	$65.1635	$65.16	$65.15	$65.20
Purchase #7	$237.86	5.306%	$250.4809	$250.48	$250.50	$250.50
7 purchase totals =	$686.17		$734.4131	$734.41	$734.45	$734.50