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	$97.99	13.673%	$111.3882	$111.39	$111.40	$111.40
Purchase #2	$137.54	4.244%	$143.3772	$143.38	$143.40	$143.40
Purchase #3	$180.67	6.243%	$191.9492	$191.95	$191.95	$191.90
Purchase #4	$113.68	13.225%	$128.7142	$128.71	$128.70	$128.70
Purchase #5	$6.85	6.714%	$7.3099	$7.31	$7.30	$7.30
Purchase #6	$148.73	6.746%	$158.7633	$158.76	$158.75	$158.80
Purchase #7	$30.56	11.811%	$34.1694	$34.17	$34.15	$34.20
7 purchase totals =	$716.02		$775.6714	$775.67	$775.65	$775.70