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	$114.70	7.385%	$123.1706	$123.17	$123.15	$123.20
Purchase #2	$97.60	13.839%	$111.1069	$111.11	$111.10	$111.10
Purchase #3	$102.43	3.347%	$105.8583	$105.86	$105.85	$105.90
Purchase #4	$184.50	6.128%	$195.8062	$195.81	$195.80	$195.80
Purchase #5	$103.72	7.311%	$111.303	$111.30	$111.30	$111.30
Purchase #6	$80.51	10.128%	$88.6641	$88.66	$88.65	$88.70
Purchase #7	$34.49	3.475%	$35.6885	$35.69	$35.70	$35.70
7 purchase totals =	$717.95		$771.5976	$771.60	$771.55	$771.70