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	$91.25	13.333%	$103.4164	$103.42	$103.40	$103.40
Purchase #2	$148.49	11.736%	$165.9168	$165.92	$165.90	$165.90
Purchase #3	$218.98	13.794%	$249.1861	$249.19	$249.20	$249.20
Purchase #4	$210.60	5.217%	$221.587	$221.59	$221.60	$221.60
Purchase #5	$142.62	7.662%	$153.5475	$153.55	$153.55	$153.50
Purchase #6	$119.29	10.626%	$131.9658	$131.97	$131.95	$132.00
Purchase #7	$59.31	5.275%	$62.4386	$62.44	$62.45	$62.40
7 purchase totals =	$990.54		$1,088.0582	$1,088.08	$1,088.05	$1,088.00