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	$227.57	12.527%	$256.0777	$256.08	$256.10	$256.10
Purchase #2	$138.30	9.494%	$151.4302	$151.43	$151.45	$151.40
Purchase #3	$72.68	6.502%	$77.4057	$77.41	$77.40	$77.40
Purchase #4	$100.77	8.838%	$109.6761	$109.68	$109.70	$109.70
Purchase #5	$238.69	5.137%	$250.9515	$250.95	$250.95	$251.00
Purchase #6	$63.46	12.713%	$71.5277	$71.53	$71.55	$71.50
Purchase #7	$32.86	4.659%	$34.3909	$34.39	$34.40	$34.40
7 purchase totals =	$874.33		$951.4598	$951.47	$951.55	$951.50