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	$236.28	9.801%	$259.4378	$259.44	$259.45	$259.40
Purchase #2	$75.58	9.605%	$82.8395	$82.84	$82.85	$82.80
Purchase #3	$130.71	9.321%	$142.8935	$142.89	$142.90	$142.90
Purchase #4	$81.88	6.712%	$87.3758	$87.38	$87.40	$87.40
Purchase #5	$114.30	9.163%	$124.7733	$124.77	$124.75	$124.80
Purchase #6	$113.32	12.493%	$127.4771	$127.48	$127.50	$127.50
Purchase #7	$48.25	13.579%	$54.8019	$54.80	$54.80	$54.80
7 purchase totals =	$800.32		$879.5989	$879.60	$879.65	$879.60