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	$7.83	9.631%	$8.5841	$8.58	$8.60	$8.60
Purchase #2	$75.35	10.874%	$83.5436	$83.54	$83.55	$83.50
Purchase #3	$90.55	6.501%	$96.4367	$96.44	$96.45	$96.40
Purchase #4	$110.44	3.472%	$114.2745	$114.27	$114.25	$114.30
Purchase #5	$45.47	9.735%	$49.8965	$49.90	$49.90	$49.90
Purchase #6	$24.61	11.594%	$27.4633	$27.46	$27.45	$27.50
Purchase #7	$175.82	7.225%	$188.523	$188.52	$188.50	$188.50
7 purchase totals =	$530.07		$568.7217	$568.71	$568.70	$568.70