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	$108.94	13.464%	$123.6077	$123.61	$123.60	$123.60
Purchase #2	$126.62	13.588%	$143.8251	$143.83	$143.85	$143.80
Purchase #3	$217.61	3.738%	$225.7443	$225.74	$225.75	$225.70
Purchase #4	$11.68	4.730%	$12.2325	$12.23	$12.25	$12.20
Purchase #5	$132.50	3.772%	$137.4979	$137.50	$137.50	$137.50
Purchase #6	$12.39	11.494%	$13.8141	$13.81	$13.80	$13.80
Purchase #7	$200.95	11.114%	$223.2836	$223.28	$223.30	$223.30
7 purchase totals =	$810.69		$880.0052	$880.00	$880.05	$879.90