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	$136.69	10.593%	$151.1696	$151.17	$151.15	$151.20
Purchase #2	$153.29	9.792%	$168.3002	$168.30	$168.30	$168.30
Purchase #3	$62.40	6.834%	$66.6644	$66.66	$66.65	$66.70
Purchase #4	$223.86	7.857%	$241.4487	$241.45	$241.45	$241.40
Purchase #5	$16.95	7.414%	$18.2067	$18.21	$18.20	$18.20
Purchase #6	$87.38	4.334%	$91.167	$91.17	$91.15	$91.20
Purchase #7	$59.51	11.521%	$66.3661	$66.37	$66.35	$66.40
7 purchase totals =	$740.08		$803.3227	$803.33	$803.25	$803.40