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	$169.51	5.564%	$178.9415	$178.94	$178.95	$178.90
Purchase #2	$112.87	3.259%	$116.5484	$116.55	$116.55	$116.50
Purchase #3	$245.87	12.214%	$275.9006	$275.90	$275.90	$275.90
Purchase #4	$244.70	11.169%	$272.0305	$272.03	$272.05	$272.00
Purchase #5	$137.44	9.772%	$150.8706	$150.87	$150.85	$150.90
Purchase #6	$153.90	12.210%	$172.6912	$172.69	$172.70	$172.70
Purchase #7	$185.87	13.308%	$210.6056	$210.61	$210.60	$210.60
7 purchase totals =	$1,250.16		$1,377.5884	$1,377.59	$1,377.60	$1,377.50