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	$110.27	5.543%	$116.3823	$116.38	$116.40	$116.40
Purchase #2	$70.75	10.679%	$78.3054	$78.31	$78.30	$78.30
Purchase #3	$216.95	10.439%	$239.5974	$239.60	$239.60	$239.60
Purchase #4	$90.72	10.805%	$100.5223	$100.52	$100.50	$100.50
Purchase #5	$150.67	9.258%	$164.619	$164.62	$164.60	$164.60
Purchase #6	$245.62	13.640%	$279.1226	$279.12	$279.10	$279.10
Purchase #7	$15.42	5.863%	$16.3241	$16.32	$16.30	$16.30
7 purchase totals =	$900.40		$994.8731	$994.87	$994.80	$994.80