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	$228.64	12.207%	$256.5501	$256.55	$256.55	$256.60
Purchase #2	$29.70	13.702%	$33.7695	$33.77	$33.75	$33.80
Purchase #3	$41.80	4.634%	$43.737	$43.74	$43.75	$43.70
Purchase #4	$238.31	7.338%	$255.7972	$255.80	$255.80	$255.80
Purchase #5	$117.69	11.640%	$131.3891	$131.39	$131.40	$131.40
Purchase #6	$38.51	9.166%	$42.0398	$42.04	$42.05	$42.00
Purchase #7	$92.27	6.721%	$98.4715	$98.47	$98.45	$98.50
7 purchase totals =	$786.92		$861.7542	$861.76	$861.75	$861.80