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	$54.92	3.333%	$56.7505	$56.75	$56.75	$56.80
Purchase #2	$214.86	13.779%	$244.4656	$244.47	$244.45	$244.50
Purchase #3	$89.92	9.510%	$98.4714	$98.47	$98.45	$98.50
Purchase #4	$199.80	10.454%	$220.6871	$220.69	$220.70	$220.70
Purchase #5	$111.40	6.368%	$118.494	$118.49	$118.50	$118.50
Purchase #6	$36.29	10.783%	$40.2032	$40.20	$40.20	$40.20
Purchase #7	$98.28	7.210%	$105.366	$105.37	$105.35	$105.40
7 purchase totals =	$805.47		$884.4378	$884.44	$884.40	$884.60