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	$80.76	8.129%	$87.325	$87.33	$87.35	$87.30
Purchase #2	$167.91	9.860%	$184.4659	$184.47	$184.45	$184.50
Purchase #3	$109.89	12.330%	$123.4394	$123.44	$123.45	$123.40
Purchase #4	$51.59	11.691%	$57.6214	$57.62	$57.60	$57.60
Purchase #5	$49.47	4.448%	$51.6704	$51.67	$51.65	$51.70
Purchase #6	$151.25	13.320%	$171.3965	$171.40	$171.40	$171.40
Purchase #7	$118.59	13.243%	$134.2949	$134.29	$134.30	$134.30
7 purchase totals =	$729.46		$810.2135	$810.22	$810.20	$810.20