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	$122.56	12.869%	$138.3322	$138.33	$138.35	$138.30
Purchase #2	$248.34	12.775%	$280.0654	$280.07	$280.05	$280.10
Purchase #3	$173.37	11.480%	$193.2729	$193.27	$193.25	$193.30
Purchase #4	$205.52	13.754%	$233.7872	$233.79	$233.80	$233.80
Purchase #5	$52.41	10.666%	$58.0001	$58.00	$58.00	$58.00
Purchase #6	$141.91	8.158%	$153.487	$153.49	$153.50	$153.50
Purchase #7	$129.98	7.326%	$139.5023	$139.50	$139.50	$139.50
7 purchase totals =	$1,074.09		$1,196.4471	$1,196.45	$1,196.45	$1,196.50