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	$109.32	12.497%	$122.9817	$122.98	$123.00	$123.00
Purchase #2	$81.73	13.250%	$92.5592	$92.56	$92.55	$92.60
Purchase #3	$178.72	9.783%	$196.2042	$196.20	$196.20	$196.20
Purchase #4	$54.55	13.255%	$61.7806	$61.78	$61.80	$61.80
Purchase #5	$14.87	6.658%	$15.86	$15.86	$15.85	$15.90
Purchase #6	$61.56	12.260%	$69.1073	$69.11	$69.10	$69.10
Purchase #7	$99.27	4.508%	$103.7451	$103.75	$103.75	$103.70
7 purchase totals =	$600.02		$662.2381	$662.24	$662.25	$662.30