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	$66.60	9.275%	$72.7772	$72.78	$72.80	$72.80
Purchase #2	$237.33	3.422%	$245.4514	$245.45	$245.45	$245.50
Purchase #3	$98.35	6.373%	$104.6178	$104.62	$104.60	$104.60
Purchase #4	$125.72	13.869%	$143.1561	$143.16	$143.15	$143.20
Purchase #5	$57.27	10.873%	$63.497	$63.50	$63.50	$63.50
Purchase #6	$173.42	10.445%	$191.5337	$191.53	$191.55	$191.50
Purchase #7	$130.65	12.525%	$147.0139	$147.01	$147.00	$147.00
7 purchase totals =	$889.34		$968.0471	$968.05	$968.05	$968.10