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	$167.77	13.486%	$190.3955	$190.40	$190.40	$190.40
Purchase #2	$126.62	9.376%	$138.4919	$138.49	$138.50	$138.50
Purchase #3	$38.74	9.630%	$42.4707	$42.47	$42.45	$42.50
Purchase #4	$85.41	6.712%	$91.1427	$91.14	$91.15	$91.10
Purchase #5	$53.77	5.150%	$56.5392	$56.54	$56.55	$56.50
Purchase #6	$16.47	8.636%	$17.8923	$17.89	$17.90	$17.90
Purchase #7	$111.82	4.804%	$117.1918	$117.19	$117.20	$117.20
7 purchase totals =	$600.60		$654.1241	$654.12	$654.15	$654.10