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	$83.96	7.341%	$90.1235	$90.12	$90.10	$90.10
Purchase #2	$15.63	6.190%	$16.5975	$16.60	$16.60	$16.60
Purchase #3	$229.82	11.141%	$255.4242	$255.42	$255.40	$255.40
Purchase #4	$219.71	7.685%	$236.5947	$236.59	$236.60	$236.60
Purchase #5	$124.88	13.486%	$141.7213	$141.72	$141.70	$141.70
Purchase #6	$43.32	5.218%	$45.5804	$45.58	$45.60	$45.60
Purchase #7	$95.60	9.868%	$105.0338	$105.03	$105.05	$105.00
7 purchase totals =	$812.92		$891.0754	$891.06	$891.05	$891.00