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	$16.93	4.262%	$17.6516	$17.65	$17.65	$17.70
Purchase #2	$168.80	13.450%	$191.5036	$191.50	$191.50	$191.50
Purchase #3	$111.36	10.732%	$123.3112	$123.31	$123.30	$123.30
Purchase #4	$56.94	13.493%	$64.6229	$64.62	$64.60	$64.60
Purchase #5	$24.54	12.703%	$27.6573	$27.66	$27.65	$27.70
Purchase #6	$58.74	6.323%	$62.4541	$62.45	$62.45	$62.50
Purchase #7	$32.44	3.276%	$33.5027	$33.50	$33.50	$33.50
7 purchase totals =	$469.75		$520.7034	$520.69	$520.65	$520.80