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	$67.84	3.216%	$70.0217	$70.02	$70.00	$70.00
Purchase #2	$208.37	12.599%	$234.6225	$234.62	$234.60	$234.60
Purchase #3	$104.31	13.299%	$118.1822	$118.18	$118.20	$118.20
Purchase #4	$66.62	7.244%	$71.446	$71.45	$71.45	$71.40
Purchase #5	$75.83	12.644%	$85.4179	$85.42	$85.40	$85.40
Purchase #6	$75.25	12.352%	$84.5449	$84.54	$84.55	$84.50
Purchase #7	$87.60	3.236%	$90.4347	$90.43	$90.45	$90.40
7 purchase totals =	$685.82		$754.6699	$754.66	$754.65	$754.50