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	$16.98	6.319%	$18.053	$18.05	$18.05	$18.10
Purchase #2	$123.25	12.861%	$139.1012	$139.10	$139.10	$139.10
Purchase #3	$21.71	4.106%	$22.6014	$22.60	$22.60	$22.60
Purchase #4	$101.45	8.800%	$110.3776	$110.38	$110.40	$110.40
Purchase #5	$218.63	9.253%	$238.8598	$238.86	$238.85	$238.90
Purchase #6	$165.93	4.361%	$173.1662	$173.17	$173.15	$173.20
Purchase #7	$92.40	12.451%	$103.9047	$103.90	$103.90	$103.90
7 purchase totals =	$740.35		$806.0639	$806.06	$806.05	$806.20