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	$49.44	6.202%	$52.5063	$52.51	$52.50	$52.50
Purchase #2	$37.55	8.391%	$40.7008	$40.70	$40.70	$40.70
Purchase #3	$49.68	9.347%	$54.3236	$54.32	$54.30	$54.30
Purchase #4	$29.88	9.715%	$32.7828	$32.78	$32.80	$32.80
Purchase #5	$225.27	9.568%	$246.8238	$246.82	$246.80	$246.80
Purchase #6	$248.70	3.120%	$256.4594	$256.46	$256.45	$256.50
Purchase #7	$101.78	11.788%	$113.7778	$113.78	$113.80	$113.80
7 purchase totals =	$742.30		$797.3745	$797.37	$797.35	$797.40