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	$42.55	7.806%	$45.8715	$45.87	$45.85	$45.90
Purchase #2	$136.58	13.798%	$155.4253	$155.43	$155.45	$155.40
Purchase #3	$83.80	6.383%	$89.149	$89.15	$89.15	$89.10
Purchase #4	$73.49	9.207%	$80.2562	$80.26	$80.25	$80.30
Purchase #5	$203.51	5.341%	$214.3795	$214.38	$214.40	$214.40
Purchase #6	$203.72	12.448%	$229.0791	$229.08	$229.10	$229.10
Purchase #7	$100.47	12.178%	$112.7052	$112.71	$112.70	$112.70
7 purchase totals =	$844.12		$926.8658	$926.88	$926.90	$926.90