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	$124.69	10.793%	$138.1478	$138.15	$138.15	$138.10
Purchase #2	$144.61	13.773%	$164.5271	$164.53	$164.55	$164.50
Purchase #3	$9.82	7.368%	$10.5435	$10.54	$10.55	$10.50
Purchase #4	$127.44	5.299%	$134.193	$134.19	$134.20	$134.20
Purchase #5	$97.94	11.754%	$109.4519	$109.45	$109.45	$109.50
Purchase #6	$59.46	7.823%	$64.1116	$64.11	$64.10	$64.10
Purchase #7	$81.87	10.798%	$90.7103	$90.71	$90.70	$90.70
7 purchase totals =	$645.83		$711.6852	$711.68	$711.70	$711.60