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	$36.50	11.167%	$40.576	$40.58	$40.60	$40.60
Purchase #2	$109.36	4.861%	$114.676	$114.68	$114.70	$114.70
Purchase #3	$183.47	13.619%	$208.4568	$208.46	$208.45	$208.50
Purchase #4	$42.94	10.196%	$47.3182	$47.32	$47.30	$47.30
Purchase #5	$43.44	5.637%	$45.8887	$45.89	$45.90	$45.90
Purchase #6	$208.26	3.643%	$215.8469	$215.85	$215.85	$215.80
Purchase #7	$92.47	12.433%	$103.9668	$103.97	$103.95	$104.00
7 purchase totals =	$716.44		$776.7294	$776.75	$776.75	$776.80