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	$71.65	9.749%	$78.6352	$78.64	$78.65	$78.60
Purchase #2	$127.58	6.794%	$136.2478	$136.25	$136.25	$136.20
Purchase #3	$34.61	10.484%	$38.2385	$38.24	$38.25	$38.20
Purchase #4	$68.75	4.445%	$71.8059	$71.81	$71.80	$71.80
Purchase #5	$229.71	4.169%	$239.2866	$239.29	$239.30	$239.30
Purchase #6	$57.54	13.649%	$65.3936	$65.39	$65.40	$65.40
Purchase #7	$247.52	9.796%	$271.7671	$271.77	$271.75	$271.80
7 purchase totals =	$837.36		$901.3747	$901.39	$901.40	$901.30