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	$42.67	6.778%	$45.5622	$45.56	$45.55	$45.60
Purchase #2	$205.39	5.772%	$217.2451	$217.25	$217.25	$217.20
Purchase #3	$47.96	12.625%	$54.015	$54.02	$54.00	$54.00
Purchase #4	$49.58	9.814%	$54.4458	$54.45	$54.45	$54.40
Purchase #5	$139.35	4.569%	$145.7169	$145.72	$145.70	$145.70
Purchase #6	$134.50	9.255%	$146.948	$146.95	$146.95	$146.90
Purchase #7	$145.73	10.419%	$160.9136	$160.91	$160.90	$160.90
7 purchase totals =	$765.18		$824.8466	$824.86	$824.80	$824.70