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	$72.50	10.396%	$80.0371	$80.04	$80.05	$80.00
Purchase #2	$243.36	6.578%	$259.3682	$259.37	$259.35	$259.40
Purchase #3	$138.97	11.606%	$155.0989	$155.10	$155.10	$155.10
Purchase #4	$24.60	3.128%	$25.3695	$25.37	$25.35	$25.40
Purchase #5	$142.80	11.534%	$159.2706	$159.27	$159.25	$159.30
Purchase #6	$200.94	11.167%	$223.379	$223.38	$223.40	$223.40
Purchase #7	$142.99	11.110%	$158.8762	$158.88	$158.90	$158.90
7 purchase totals =	$966.16		$1,061.3995	$1,061.41	$1,061.40	$1,061.50