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	$32.37	3.694%	$33.5657	$33.57	$33.55	$33.60
Purchase #2	$112.57	13.659%	$127.9459	$127.95	$127.95	$127.90
Purchase #3	$208.32	6.703%	$222.2837	$222.28	$222.30	$222.30
Purchase #4	$121.68	13.757%	$138.4195	$138.42	$138.40	$138.40
Purchase #5	$90.93	10.796%	$100.7468	$100.75	$100.75	$100.70
Purchase #6	$133.99	10.398%	$147.9223	$147.92	$147.90	$147.90
Purchase #7	$170.54	11.749%	$190.5767	$190.58	$190.60	$190.60
7 purchase totals =	$870.40		$961.4606	$961.47	$961.45	$961.40