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	$49.44	12.618%	$55.6783	$55.68	$55.70	$55.70
Purchase #2	$25.45	13.855%	$28.9761	$28.98	$29.00	$29.00
Purchase #3	$54.90	11.724%	$61.3365	$61.34	$61.35	$61.30
Purchase #4	$244.33	12.352%	$274.5096	$274.51	$274.50	$274.50
Purchase #5	$48.71	10.215%	$53.6857	$53.69	$53.70	$53.70
Purchase #6	$58.63	5.382%	$61.7855	$61.79	$61.80	$61.80
Purchase #7	$92.35	11.833%	$103.2778	$103.28	$103.30	$103.30
7 purchase totals =	$573.81		$639.2495	$639.27	$639.35	$639.30