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	$171.28	11.852%	$191.5801	$191.58	$191.60	$191.60
Purchase #2	$189.43	11.201%	$210.6481	$210.65	$210.65	$210.60
Purchase #3	$171.28	4.812%	$179.522	$179.52	$179.50	$179.50
Purchase #4	$22.72	8.145%	$24.5705	$24.57	$24.55	$24.60
Purchase #5	$85.37	5.603%	$90.1533	$90.15	$90.15	$90.20
Purchase #6	$164.60	6.241%	$174.8727	$174.87	$174.85	$174.90
Purchase #7	$26.38	13.489%	$29.9384	$29.94	$29.95	$29.90
7 purchase totals =	$831.06		$901.2851	$901.28	$901.25	$901.30