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	$123.48	13.195%	$139.7732	$139.77	$139.75	$139.80
Purchase #2	$94.82	8.328%	$102.7166	$102.72	$102.70	$102.70
Purchase #3	$144.61	9.838%	$158.8367	$158.84	$158.85	$158.80
Purchase #4	$95.71	10.254%	$105.5241	$105.52	$105.50	$105.50
Purchase #5	$215.26	11.682%	$240.4067	$240.41	$240.40	$240.40
Purchase #6	$246.94	3.596%	$255.82	$255.82	$255.80	$255.80
Purchase #7	$191.94	8.224%	$207.7251	$207.73	$207.75	$207.70
7 purchase totals =	$1,112.76		$1,210.8024	$1,210.81	$1,210.75	$1,210.70