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	$139.45	7.772%	$150.2881	$150.29	$150.30	$150.30
Purchase #2	$170.27	12.600%	$191.724	$191.72	$191.70	$191.70
Purchase #3	$237.42	7.714%	$255.7346	$255.73	$255.75	$255.70
Purchase #4	$169.97	10.411%	$187.6656	$187.67	$187.65	$187.70
Purchase #5	$34.73	7.628%	$37.3792	$37.38	$37.40	$37.40
Purchase #6	$152.37	5.689%	$161.0383	$161.04	$161.05	$161.00
Purchase #7	$28.93	7.730%	$31.1663	$31.17	$31.15	$31.20
7 purchase totals =	$933.14		$1,014.9961	$1,015.00	$1,015.00	$1,015.00