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	$33.93	3.841%	$35.2333	$35.23	$35.25	$35.20
Purchase #2	$105.82	11.874%	$118.3851	$118.39	$118.40	$118.40
Purchase #3	$180.28	11.386%	$200.8067	$200.81	$200.80	$200.80
Purchase #4	$158.62	13.757%	$180.4414	$180.44	$180.45	$180.40
Purchase #5	$45.68	6.154%	$48.4911	$48.49	$48.50	$48.50
Purchase #6	$51.42	7.339%	$55.1937	$55.19	$55.20	$55.20
Purchase #7	$11.70	5.236%	$12.3126	$12.31	$12.30	$12.30
7 purchase totals =	$587.45		$650.8639	$650.86	$650.90	$650.80