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	$100.80	13.316%	$114.2225	$114.22	$114.20	$114.20
Purchase #2	$92.58	8.628%	$100.5678	$100.57	$100.55	$100.60
Purchase #3	$36.28	10.575%	$40.1166	$40.12	$40.10	$40.10
Purchase #4	$199.43	10.780%	$220.9286	$220.93	$220.95	$220.90
Purchase #5	$119.47	11.594%	$133.3214	$133.32	$133.30	$133.30
Purchase #6	$45.93	8.570%	$49.8662	$49.87	$49.85	$49.90
Purchase #7	$172.40	8.171%	$186.4868	$186.49	$186.50	$186.50
7 purchase totals =	$766.89		$845.5099	$845.52	$845.45	$845.50