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	$112.50	5.601%	$118.8011	$118.80	$118.80	$118.80
Purchase #2	$88.77	4.113%	$92.4211	$92.42	$92.40	$92.40
Purchase #3	$65.38	10.380%	$72.1664	$72.17	$72.15	$72.20
Purchase #4	$118.53	10.626%	$131.125	$131.13	$131.15	$131.10
Purchase #5	$121.80	4.512%	$127.2956	$127.30	$127.30	$127.30
Purchase #6	$47.52	7.480%	$51.0745	$51.07	$51.05	$51.10
Purchase #7	$15.63	5.122%	$16.4306	$16.43	$16.45	$16.40
7 purchase totals =	$570.13		$609.3143	$609.32	$609.30	$609.30