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	$71.72	12.390%	$80.6061	$80.61	$80.60	$80.60
Purchase #2	$138.58	3.629%	$143.6091	$143.61	$143.60	$143.60
Purchase #3	$62.28	10.453%	$68.7901	$68.79	$68.80	$68.80
Purchase #4	$164.88	12.321%	$185.1949	$185.19	$185.20	$185.20
Purchase #5	$95.37	13.522%	$108.2659	$108.27	$108.25	$108.30
Purchase #6	$122.77	12.776%	$138.4551	$138.46	$138.45	$138.50
Purchase #7	$79.53	13.207%	$90.0335	$90.03	$90.05	$90.00
7 purchase totals =	$735.13		$814.9547	$814.96	$814.95	$815.00