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	$109.62	12.624%	$123.4584	$123.46	$123.45	$123.50
Purchase #2	$114.30	10.622%	$126.4409	$126.44	$126.45	$126.40
Purchase #3	$116.50	9.360%	$127.4044	$127.40	$127.40	$127.40
Purchase #4	$215.45	7.489%	$231.5851	$231.59	$231.60	$231.60
Purchase #5	$118.74	4.345%	$123.8993	$123.90	$123.90	$123.90
Purchase #6	$109.40	8.691%	$118.908	$118.91	$118.90	$118.90
Purchase #7	$91.34	12.702%	$102.942	$102.94	$102.95	$102.90
7 purchase totals =	$875.35		$954.6381	$954.64	$954.65	$954.60