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	$57.60	13.381%	$65.3075	$65.31	$65.30	$65.30
Purchase #2	$98.99	6.103%	$105.0314	$105.03	$105.05	$105.00
Purchase #3	$196.86	9.551%	$215.6621	$215.66	$215.65	$215.70
Purchase #4	$192.88	12.575%	$217.1347	$217.13	$217.15	$217.10
Purchase #5	$90.74	11.464%	$101.1424	$101.14	$101.15	$101.10
Purchase #6	$5.34	3.378%	$5.5204	$5.52	$5.50	$5.50
Purchase #7	$112.54	13.328%	$127.5393	$127.54	$127.55	$127.50
7 purchase totals =	$754.95		$837.3378	$837.33	$837.35	$837.20