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	$117.71	10.716%	$130.3238	$130.32	$130.30	$130.30
Purchase #2	$207.28	10.243%	$228.5117	$228.51	$228.50	$228.50
Purchase #3	$183.52	4.232%	$191.2866	$191.29	$191.30	$191.30
Purchase #4	$119.66	7.403%	$128.5184	$128.52	$128.50	$128.50
Purchase #5	$165.69	10.120%	$182.4578	$182.46	$182.45	$182.50
Purchase #6	$21.45	11.191%	$23.8505	$23.85	$23.85	$23.90
Purchase #7	$100.65	3.631%	$104.3046	$104.30	$104.30	$104.30
7 purchase totals =	$915.96		$989.2534	$989.25	$989.20	$989.30