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	$138.80	4.746%	$145.3874	$145.39	$145.40	$145.40
Purchase #2	$242.99	9.613%	$266.3486	$266.35	$266.35	$266.30
Purchase #3	$43.78	8.216%	$47.377	$47.38	$47.40	$47.40
Purchase #4	$138.89	10.754%	$153.8262	$153.83	$153.85	$153.80
Purchase #5	$152.61	4.279%	$159.1402	$159.14	$159.15	$159.10
Purchase #6	$46.89	9.666%	$51.4224	$51.42	$51.40	$51.40
Purchase #7	$163.29	13.620%	$185.5301	$185.53	$185.55	$185.50
7 purchase totals =	$927.25		$1,009.0319	$1,009.04	$1,009.10	$1,008.90