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	$51.39	11.224%	$57.158	$57.16	$57.15	$57.20
Purchase #2	$166.85	6.716%	$178.0556	$178.06	$178.05	$178.10
Purchase #3	$50.45	8.132%	$54.5526	$54.55	$54.55	$54.60
Purchase #4	$109.58	13.505%	$124.3788	$124.38	$124.40	$124.40
Purchase #5	$144.57	7.563%	$155.5038	$155.50	$155.50	$155.50
Purchase #6	$186.49	11.798%	$208.4921	$208.49	$208.50	$208.50
Purchase #7	$29.71	9.576%	$32.555	$32.56	$32.55	$32.60
7 purchase totals =	$739.04		$810.6959	$810.70	$810.70	$810.90