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	$12.51	10.766%	$13.8568	$13.86	$13.85	$13.90
Purchase #2	$130.71	13.655%	$148.5585	$148.56	$148.55	$148.60
Purchase #3	$97.27	6.822%	$103.9058	$103.91	$103.90	$103.90
Purchase #4	$28.67	13.704%	$32.5989	$32.60	$32.60	$32.60
Purchase #5	$130.80	4.223%	$136.3237	$136.32	$136.30	$136.30
Purchase #6	$163.43	10.186%	$180.077	$180.08	$180.10	$180.10
Purchase #7	$143.59	12.237%	$161.1611	$161.16	$161.15	$161.20
7 purchase totals =	$706.98		$776.4818	$776.49	$776.45	$776.60