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	$232.62	11.542%	$259.469	$259.47	$259.45	$259.50
Purchase #2	$28.90	12.699%	$32.57	$32.57	$32.55	$32.60
Purchase #3	$202.81	12.509%	$228.1795	$228.18	$228.20	$228.20
Purchase #4	$172.97	3.110%	$178.3494	$178.35	$178.35	$178.30
Purchase #5	$105.87	9.822%	$116.2686	$116.27	$116.25	$116.30
Purchase #6	$47.30	11.464%	$52.7225	$52.72	$52.70	$52.70
Purchase #7	$250.69	9.225%	$273.8162	$273.82	$273.80	$273.80
7 purchase totals =	$1,041.16		$1,141.3752	$1,141.38	$1,141.30	$1,141.40