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	$224.35	13.322%	$254.2379	$254.24	$254.25	$254.20
Purchase #2	$223.74	10.852%	$248.0203	$248.02	$248.00	$248.00
Purchase #3	$112.82	7.334%	$121.0942	$121.09	$121.10	$121.10
Purchase #4	$144.37	13.243%	$163.4889	$163.49	$163.50	$163.50
Purchase #5	$79.60	13.443%	$90.3006	$90.30	$90.30	$90.30
Purchase #6	$81.27	10.449%	$89.7619	$89.76	$89.75	$89.80
Purchase #7	$114.32	10.758%	$126.6185	$126.62	$126.60	$126.60
7 purchase totals =	$980.47		$1,093.5223	$1,093.52	$1,093.50	$1,093.50