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	$189.62	5.727%	$200.4795	$200.48	$200.50	$200.50
Purchase #2	$113.35	12.325%	$127.3204	$127.32	$127.30	$127.30
Purchase #3	$178.85	5.497%	$188.6814	$188.68	$188.70	$188.70
Purchase #4	$77.97	6.469%	$83.0139	$83.01	$83.00	$83.00
Purchase #5	$47.68	8.152%	$51.5669	$51.57	$51.55	$51.60
Purchase #6	$107.97	10.522%	$119.3306	$119.33	$119.35	$119.30
Purchase #7	$59.81	3.141%	$61.6886	$61.69	$61.70	$61.70
7 purchase totals =	$775.25		$832.0813	$832.08	$832.10	$832.10