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	$16.59	5.599%	$17.5189	$17.52	$17.50	$17.50
Purchase #2	$90.74	4.229%	$94.5774	$94.58	$94.60	$94.60
Purchase #3	$10.82	10.320%	$11.9366	$11.94	$11.95	$11.90
Purchase #4	$138.93	3.286%	$143.4952	$143.50	$143.50	$143.50
Purchase #5	$98.48	12.229%	$110.5231	$110.52	$110.50	$110.50
Purchase #6	$130.29	10.690%	$144.218	$144.22	$144.20	$144.20
Purchase #7	$216.69	11.275%	$241.1218	$241.12	$241.10	$241.10
7 purchase totals =	$702.54		$763.3910	$763.40	$763.35	$763.30