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	$36.59	9.793%	$40.1733	$40.17	$40.15	$40.20
Purchase #2	$13.97	9.805%	$15.3398	$15.34	$15.35	$15.30
Purchase #3	$207.34	7.168%	$222.2021	$222.20	$222.20	$222.20
Purchase #4	$184.31	13.189%	$208.6186	$208.62	$208.60	$208.60
Purchase #5	$98.76	12.580%	$111.184	$111.18	$111.20	$111.20
Purchase #6	$39.52	5.650%	$41.7529	$41.75	$41.75	$41.80
Purchase #7	$51.25	8.496%	$55.6042	$55.60	$55.60	$55.60
7 purchase totals =	$631.74		$694.8749	$694.86	$694.85	$694.90