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	$15.97	9.120%	$17.4265	$17.43	$17.45	$17.40
Purchase #2	$217.40	6.356%	$231.2179	$231.22	$231.20	$231.20
Purchase #3	$99.38	5.280%	$104.6273	$104.63	$104.65	$104.60
Purchase #4	$146.82	12.852%	$165.6893	$165.69	$165.70	$165.70
Purchase #5	$148.82	3.275%	$153.6939	$153.69	$153.70	$153.70
Purchase #6	$77.36	12.439%	$86.9828	$86.98	$87.00	$87.00
Purchase #7	$244.50	4.537%	$255.593	$255.59	$255.60	$255.60
7 purchase totals =	$950.25		$1,015.2307	$1,015.23	$1,015.30	$1,015.20