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	$16.98	13.356%	$19.2478	$19.25	$19.25	$19.20
Purchase #2	$144.41	5.132%	$151.8211	$151.82	$151.80	$151.80
Purchase #3	$104.31	7.210%	$111.8308	$111.83	$111.85	$111.80
Purchase #4	$66.37	13.276%	$75.1813	$75.18	$75.20	$75.20
Purchase #5	$26.89	5.761%	$28.4391	$28.44	$28.45	$28.40
Purchase #6	$194.95	5.459%	$205.5923	$205.59	$205.60	$205.60
Purchase #7	$64.66	12.361%	$72.6526	$72.65	$72.65	$72.70
7 purchase totals =	$618.57		$664.7650	$664.76	$664.80	$664.70