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	$126.94	13.390%	$143.9373	$143.94	$143.95	$143.90
Purchase #2	$103.45	13.263%	$117.1706	$117.17	$117.15	$117.20
Purchase #3	$247.71	10.312%	$273.2539	$273.25	$273.25	$273.30
Purchase #4	$155.87	10.372%	$172.0368	$172.04	$172.05	$172.00
Purchase #5	$90.38	12.538%	$101.7118	$101.71	$101.70	$101.70
Purchase #6	$238.71	11.232%	$265.5219	$265.52	$265.50	$265.50
Purchase #7	$39.52	13.408%	$44.8188	$44.82	$44.80	$44.80
7 purchase totals =	$1,002.58		$1,118.4511	$1,118.45	$1,118.40	$1,118.40