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	$51.30	12.755%	$57.8433	$57.84	$57.85	$57.80
Purchase #2	$163.66	6.608%	$174.4747	$174.47	$174.45	$174.50
Purchase #3	$17.78	4.208%	$18.5282	$18.53	$18.55	$18.50
Purchase #4	$123.47	13.422%	$140.0421	$140.04	$140.05	$140.00
Purchase #5	$139.51	8.605%	$151.5148	$151.51	$151.50	$151.50
Purchase #6	$30.30	7.636%	$32.6137	$32.61	$32.60	$32.60
Purchase #7	$129.68	10.152%	$142.8451	$142.85	$142.85	$142.80
7 purchase totals =	$655.70		$717.8619	$717.85	$717.85	$717.70