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	$242.27	5.439%	$255.4471	$255.45	$255.45	$255.40
Purchase #2	$65.56	10.475%	$72.4274	$72.43	$72.45	$72.40
Purchase #3	$61.45	8.299%	$66.5497	$66.55	$66.55	$66.50
Purchase #4	$83.57	7.203%	$89.5895	$89.59	$89.60	$89.60
Purchase #5	$190.82	10.722%	$211.2797	$211.28	$211.30	$211.30
Purchase #6	$65.82	4.306%	$68.6542	$68.65	$68.65	$68.70
Purchase #7	$87.33	11.716%	$97.5616	$97.56	$97.55	$97.60
7 purchase totals =	$796.82		$861.5092	$861.51	$861.55	$861.50