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	$10.38	9.783%	$11.3955	$11.40	$11.40	$11.40
Purchase #2	$241.44	10.428%	$266.6174	$266.62	$266.60	$266.60
Purchase #3	$34.87	13.410%	$39.5461	$39.55	$39.55	$39.50
Purchase #4	$51.54	9.640%	$56.5085	$56.51	$56.50	$56.50
Purchase #5	$52.66	13.559%	$59.8002	$59.80	$59.80	$59.80
Purchase #6	$212.54	7.684%	$228.8716	$228.87	$228.85	$228.90
Purchase #7	$125.52	4.298%	$130.9148	$130.91	$130.90	$130.90
7 purchase totals =	$728.95		$793.6541	$793.66	$793.60	$793.60