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	$160.48	12.364%	$180.3217	$180.32	$180.30	$180.30
Purchase #2	$29.87	4.230%	$31.1335	$31.13	$31.15	$31.10
Purchase #3	$70.53	8.394%	$76.4503	$76.45	$76.45	$76.50
Purchase #4	$249.50	4.397%	$260.4705	$260.47	$260.45	$260.50
Purchase #5	$26.74	7.622%	$28.7781	$28.78	$28.80	$28.80
Purchase #6	$156.30	5.298%	$164.5808	$164.58	$164.60	$164.60
Purchase #7	$240.54	10.625%	$266.0974	$266.10	$266.10	$266.10
7 purchase totals =	$933.96		$1,007.8323	$1,007.83	$1,007.85	$1,007.90