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	$105.82	13.626%	$120.239	$120.24	$120.25	$120.20
Purchase #2	$44.78	10.279%	$49.3829	$49.38	$49.40	$49.40
Purchase #3	$70.60	10.687%	$78.145	$78.15	$78.15	$78.10
Purchase #4	$72.86	11.368%	$81.1427	$81.14	$81.15	$81.10
Purchase #5	$59.68	11.491%	$66.5378	$66.54	$66.55	$66.50
Purchase #6	$248.92	10.305%	$274.5712	$274.57	$274.55	$274.60
Purchase #7	$16.83	7.740%	$18.1326	$18.13	$18.15	$18.10
7 purchase totals =	$619.49		$688.1512	$688.15	$688.20	$688.00