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	$115.96	13.392%	$131.4894	$131.49	$131.50	$131.50
Purchase #2	$198.29	11.582%	$221.2559	$221.26	$221.25	$221.30
Purchase #3	$79.81	3.583%	$82.6696	$82.67	$82.65	$82.70
Purchase #4	$134.70	8.757%	$146.4957	$146.50	$146.50	$146.50
Purchase #5	$79.64	10.857%	$88.2865	$88.29	$88.30	$88.30
Purchase #6	$63.78	4.770%	$66.8223	$66.82	$66.80	$66.80
Purchase #7	$169.52	13.488%	$192.3849	$192.38	$192.40	$192.40
7 purchase totals =	$841.70		$929.4043	$929.41	$929.40	$929.50