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	$125.29	12.138%	$140.4977	$140.50	$140.50	$140.50
Purchase #2	$62.46	5.764%	$66.0602	$66.06	$66.05	$66.10
Purchase #3	$205.92	8.412%	$223.242	$223.24	$223.25	$223.20
Purchase #4	$213.45	4.841%	$223.7831	$223.78	$223.80	$223.80
Purchase #5	$166.59	12.407%	$187.2588	$187.26	$187.25	$187.30
Purchase #6	$238.93	6.587%	$254.6683	$254.67	$254.65	$254.70
Purchase #7	$119.49	6.840%	$127.6631	$127.66	$127.65	$127.70
7 purchase totals =	$1,132.13		$1,223.1732	$1,223.17	$1,223.15	$1,223.30