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	$40.58	7.393%	$43.5801	$43.58	$43.60	$43.60
Purchase #2	$102.69	12.157%	$115.174	$115.17	$115.15	$115.20
Purchase #3	$124.38	11.865%	$139.1377	$139.14	$139.15	$139.10
Purchase #4	$156.39	7.210%	$167.6657	$167.67	$167.65	$167.70
Purchase #5	$80.28	12.134%	$90.0212	$90.02	$90.00	$90.00
Purchase #6	$119.29	4.161%	$124.2537	$124.25	$124.25	$124.30
Purchase #7	$89.91	6.186%	$95.4718	$95.47	$95.45	$95.50
7 purchase totals =	$713.52		$775.3042	$775.30	$775.25	$775.40