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	$17.98	11.833%	$20.1076	$20.11	$20.10	$20.10
Purchase #2	$150.74	4.769%	$157.9288	$157.93	$157.95	$157.90
Purchase #3	$38.69	11.758%	$43.2392	$43.24	$43.25	$43.20
Purchase #4	$40.45	11.801%	$45.2235	$45.22	$45.20	$45.20
Purchase #5	$74.37	5.714%	$78.6195	$78.62	$78.60	$78.60
Purchase #6	$126.39	10.730%	$139.9516	$139.95	$139.95	$140.00
Purchase #7	$220.55	7.597%	$237.3052	$237.31	$237.30	$237.30
7 purchase totals =	$669.17		$722.3754	$722.38	$722.35	$722.30