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	$53.78	10.629%	$59.4963	$59.50	$59.50	$59.50
Purchase #2	$168.58	6.660%	$179.8074	$179.81	$179.80	$179.80
Purchase #3	$16.95	11.845%	$18.9577	$18.96	$18.95	$19.00
Purchase #4	$118.29	12.564%	$133.152	$133.15	$133.15	$133.20
Purchase #5	$44.65	7.264%	$47.8934	$47.89	$47.90	$47.90
Purchase #6	$20.76	12.314%	$23.3164	$23.32	$23.30	$23.30
Purchase #7	$52.71	6.255%	$56.007	$56.01	$56.00	$56.00
7 purchase totals =	$475.72		$518.6302	$518.64	$518.60	$518.70