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	$227.45	10.669%	$251.7166	$251.72	$251.70	$251.70
Purchase #2	$132.82	9.156%	$144.981	$144.98	$145.00	$145.00
Purchase #3	$105.43	11.109%	$117.1422	$117.14	$117.15	$117.10
Purchase #4	$166.85	11.218%	$185.5672	$185.57	$185.55	$185.60
Purchase #5	$168.35	6.127%	$178.6648	$178.66	$178.65	$178.70
Purchase #6	$70.35	13.751%	$80.0238	$80.02	$80.00	$80.00
Purchase #7	$182.98	9.705%	$200.7382	$200.74	$200.75	$200.70
7 purchase totals =	$1,054.23		$1,158.8338	$1,158.83	$1,158.80	$1,158.80