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	$139.45	5.155%	$146.6386	$146.64	$146.65	$146.60
Purchase #2	$158.35	13.681%	$180.0139	$180.01	$180.00	$180.00
Purchase #3	$18.42	10.845%	$20.4176	$20.42	$20.40	$20.40
Purchase #4	$9.42	11.225%	$10.4774	$10.48	$10.50	$10.50
Purchase #5	$168.90	6.289%	$179.5221	$179.52	$179.50	$179.50
Purchase #6	$80.99	11.413%	$90.2334	$90.23	$90.25	$90.20
Purchase #7	$38.61	12.150%	$43.3011	$43.30	$43.30	$43.30
7 purchase totals =	$614.14		$670.6041	$670.60	$670.60	$670.50