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	$244.51	7.782%	$263.5378	$263.54	$263.55	$263.50
Purchase #2	$210.92	6.287%	$224.1805	$224.18	$224.20	$224.20
Purchase #3	$81.90	10.667%	$90.6363	$90.64	$90.65	$90.60
Purchase #4	$211.51	9.491%	$231.5844	$231.58	$231.60	$231.60
Purchase #5	$64.52	11.600%	$72.0043	$72.00	$72.00	$72.00
Purchase #6	$231.73	11.748%	$258.9536	$258.95	$258.95	$259.00
Purchase #7	$100.36	12.757%	$113.1629	$113.16	$113.15	$113.20
7 purchase totals =	$1,145.45		$1,254.0598	$1,254.05	$1,254.10	$1,254.10