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	$134.36	11.581%	$149.9202	$149.92	$149.90	$149.90
Purchase #2	$116.29	13.799%	$132.3369	$132.34	$132.35	$132.30
Purchase #3	$20.51	6.783%	$21.9012	$21.90	$21.90	$21.90
Purchase #4	$105.31	10.675%	$116.5518	$116.55	$116.55	$116.60
Purchase #5	$25.60	9.754%	$28.097	$28.10	$28.10	$28.10
Purchase #6	$238.85	5.700%	$252.4645	$252.46	$252.45	$252.50
Purchase #7	$136.46	5.683%	$144.215	$144.22	$144.20	$144.20
7 purchase totals =	$777.38		$845.4866	$845.49	$845.45	$845.50