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	$27.57	3.257%	$28.468	$28.47	$28.45	$28.50
Purchase #2	$70.62	11.240%	$78.5577	$78.56	$78.55	$78.60
Purchase #3	$49.70	5.172%	$52.2705	$52.27	$52.25	$52.30
Purchase #4	$65.36	12.594%	$73.5914	$73.59	$73.60	$73.60
Purchase #5	$240.36	7.613%	$258.6586	$258.66	$258.65	$258.70
Purchase #6	$53.58	8.801%	$58.2956	$58.30	$58.30	$58.30
Purchase #7	$31.82	10.649%	$35.2085	$35.21	$35.20	$35.20
7 purchase totals =	$539.01		$585.0503	$585.06	$585.00	$585.20