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	$39.32	7.406%	$42.232	$42.23	$42.25	$42.20
Purchase #2	$246.62	5.253%	$259.5749	$259.57	$259.55	$259.60
Purchase #3	$203.88	11.472%	$227.2691	$227.27	$227.25	$227.30
Purchase #4	$166.82	3.510%	$172.6754	$172.68	$172.70	$172.70
Purchase #5	$185.27	6.636%	$197.5645	$197.56	$197.55	$197.60
Purchase #6	$231.97	9.160%	$253.2185	$253.22	$253.20	$253.20
Purchase #7	$19.93	6.838%	$21.2928	$21.29	$21.30	$21.30
7 purchase totals =	$1,093.81		$1,173.8272	$1,173.82	$1,173.80	$1,173.90