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	$24.69	11.251%	$27.4679	$27.47	$27.45	$27.50
Purchase #2	$111.69	12.851%	$126.0433	$126.04	$126.05	$126.00
Purchase #3	$70.80	10.177%	$78.0053	$78.01	$78.00	$78.00
Purchase #4	$107.60	3.760%	$111.6458	$111.65	$111.65	$111.60
Purchase #5	$131.69	8.856%	$143.3525	$143.35	$143.35	$143.40
Purchase #6	$57.59	6.430%	$61.293	$61.29	$61.30	$61.30
Purchase #7	$40.94	3.114%	$42.2149	$42.21	$42.20	$42.20
7 purchase totals =	$545.00		$590.0227	$590.02	$590.00	$590.00