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	$49.95	6.680%	$53.2867	$53.29	$53.30	$53.30
Purchase #2	$111.89	3.815%	$116.1586	$116.16	$116.15	$116.20
Purchase #3	$14.65	8.416%	$15.8829	$15.88	$15.90	$15.90
Purchase #4	$16.49	10.799%	$18.2708	$18.27	$18.25	$18.30
Purchase #5	$52.49	12.660%	$59.1352	$59.14	$59.15	$59.10
Purchase #6	$211.96	7.391%	$227.626	$227.63	$227.65	$227.60
Purchase #7	$113.46	3.702%	$117.6603	$117.66	$117.65	$117.70
7 purchase totals =	$570.89		$608.0205	$608.03	$608.05	$608.10