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	$90.68	10.321%	$100.0391	$100.04	$100.05	$100.00
Purchase #2	$201.66	13.357%	$228.5957	$228.60	$228.60	$228.60
Purchase #3	$155.67	10.443%	$171.9266	$171.93	$171.95	$171.90
Purchase #4	$172.73	7.579%	$185.8212	$185.82	$185.80	$185.80
Purchase #5	$157.82	8.593%	$171.3815	$171.38	$171.40	$171.40
Purchase #6	$100.46	13.715%	$114.2381	$114.24	$114.25	$114.20
Purchase #7	$107.93	11.729%	$120.5891	$120.59	$120.60	$120.60
7 purchase totals =	$986.95		$1,092.5913	$1,092.60	$1,092.65	$1,092.50