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	$103.78	5.358%	$109.3405	$109.34	$109.35	$109.30
Purchase #2	$206.91	12.630%	$233.0427	$233.04	$233.05	$233.00
Purchase #3	$126.42	13.681%	$143.7155	$143.72	$143.70	$143.70
Purchase #4	$215.43	12.234%	$241.7857	$241.79	$241.80	$241.80
Purchase #5	$175.60	4.661%	$183.7847	$183.78	$183.80	$183.80
Purchase #6	$132.38	9.810%	$145.3665	$145.37	$145.35	$145.40
Purchase #7	$97.31	11.407%	$108.4102	$108.41	$108.40	$108.40
7 purchase totals =	$1,057.83		$1,165.4458	$1,165.45	$1,165.45	$1,165.40