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	$57.44	6.869%	$61.3856	$61.39	$61.40	$61.40
Purchase #2	$233.56	9.173%	$254.9845	$254.98	$255.00	$255.00
Purchase #3	$74.87	4.801%	$78.4645	$78.46	$78.45	$78.50
Purchase #4	$111.75	10.453%	$123.4312	$123.43	$123.45	$123.40
Purchase #5	$227.40	11.369%	$253.2531	$253.25	$253.25	$253.30
Purchase #6	$197.72	12.830%	$223.0875	$223.09	$223.10	$223.10
Purchase #7	$102.68	13.140%	$116.1722	$116.17	$116.15	$116.20
7 purchase totals =	$1,005.42		$1,110.7786	$1,110.77	$1,110.80	$1,110.90