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	$65.51	10.326%	$72.2746	$72.27	$72.25	$72.30
Purchase #2	$218.91	4.137%	$227.9663	$227.97	$227.95	$228.00
Purchase #3	$9.98	9.411%	$10.9192	$10.92	$10.90	$10.90
Purchase #4	$79.34	13.643%	$90.1644	$90.16	$90.15	$90.20
Purchase #5	$135.94	3.758%	$141.0486	$141.05	$141.05	$141.00
Purchase #6	$61.27	9.387%	$67.0214	$67.02	$67.00	$67.00
Purchase #7	$36.60	5.171%	$38.4926	$38.49	$38.50	$38.50
7 purchase totals =	$607.55		$647.8871	$647.88	$647.80	$647.90