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	$143.27	10.366%	$158.1214	$158.12	$158.10	$158.10
Purchase #2	$232.59	9.813%	$255.4141	$255.41	$255.40	$255.40
Purchase #3	$150.95	11.611%	$168.4768	$168.48	$168.50	$168.50
Purchase #4	$72.86	9.783%	$79.9879	$79.99	$80.00	$80.00
Purchase #5	$152.94	3.699%	$158.5973	$158.60	$158.60	$158.60
Purchase #6	$90.76	13.297%	$102.8284	$102.83	$102.85	$102.80
Purchase #7	$12.85	7.615%	$13.8285	$13.83	$13.85	$13.80
7 purchase totals =	$856.22		$937.2544	$937.26	$937.30	$937.20