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	$52.78	3.128%	$54.431	$54.43	$54.45	$54.40
Purchase #2	$44.78	9.691%	$49.1196	$49.12	$49.10	$49.10
Purchase #3	$180.82	4.392%	$188.7616	$188.76	$188.75	$188.80
Purchase #4	$101.62	12.723%	$114.5491	$114.55	$114.55	$114.50
Purchase #5	$154.28	6.527%	$164.3499	$164.35	$164.35	$164.30
Purchase #6	$248.62	8.704%	$270.2599	$270.26	$270.25	$270.30
Purchase #7	$56.37	4.758%	$59.0521	$59.05	$59.05	$59.10
7 purchase totals =	$839.27		$900.5232	$900.52	$900.50	$900.50