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	$9.53	7.784%	$10.2718	$10.27	$10.25	$10.30
Purchase #2	$240.45	6.418%	$255.8821	$255.88	$255.90	$255.90
Purchase #3	$108.33	7.589%	$116.5512	$116.55	$116.55	$116.60
Purchase #4	$141.85	7.490%	$152.4746	$152.47	$152.45	$152.50
Purchase #5	$192.51	7.851%	$207.624	$207.62	$207.60	$207.60
Purchase #6	$100.77	8.303%	$109.1369	$109.14	$109.15	$109.10
Purchase #7	$34.32	9.725%	$37.6576	$37.66	$37.65	$37.70
7 purchase totals =	$827.76		$889.5982	$889.59	$889.55	$889.70