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	$51.64	13.233%	$58.4735	$58.47	$58.45	$58.50
Purchase #2	$196.27	13.123%	$222.0265	$222.03	$222.05	$222.00
Purchase #3	$22.39	10.217%	$24.6776	$24.68	$24.70	$24.70
Purchase #4	$237.31	8.127%	$256.5962	$256.60	$256.60	$256.60
Purchase #5	$49.60	6.160%	$52.6554	$52.66	$52.65	$52.70
Purchase #6	$148.35	10.855%	$164.4534	$164.45	$164.45	$164.50
Purchase #7	$178.72	11.208%	$198.7509	$198.75	$198.75	$198.80
7 purchase totals =	$884.28		$977.6335	$977.64	$977.65	$977.80