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	$18.82	10.634%	$20.8213	$20.82	$20.80	$20.80
Purchase #2	$83.53	7.299%	$89.6269	$89.63	$89.65	$89.60
Purchase #3	$8.89	4.449%	$9.2855	$9.29	$9.30	$9.30
Purchase #4	$36.45	3.865%	$37.8588	$37.86	$37.85	$37.90
Purchase #5	$239.30	5.489%	$252.4352	$252.44	$252.45	$252.40
Purchase #6	$125.56	10.391%	$138.6069	$138.61	$138.60	$138.60
Purchase #7	$71.35	9.730%	$78.2924	$78.29	$78.30	$78.30
7 purchase totals =	$583.90		$626.9270	$626.94	$626.95	$626.90