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	$55.49	10.285%	$61.1971	$61.20	$61.20	$61.20
Purchase #2	$34.73	8.430%	$37.6577	$37.66	$37.65	$37.70
Purchase #3	$225.48	11.663%	$251.7777	$251.78	$251.80	$251.80
Purchase #4	$116.66	6.127%	$123.8078	$123.81	$123.80	$123.80
Purchase #5	$47.60	10.201%	$52.4557	$52.46	$52.45	$52.50
Purchase #6	$153.32	9.638%	$168.097	$168.10	$168.10	$168.10
Purchase #7	$198.82	13.375%	$225.4122	$225.41	$225.40	$225.40
7 purchase totals =	$832.10		$920.4052	$920.42	$920.40	$920.50