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	$9.38	9.760%	$10.2955	$10.30	$10.30	$10.30
Purchase #2	$154.50	6.360%	$164.3262	$164.33	$164.35	$164.30
Purchase #3	$236.89	8.608%	$257.2815	$257.28	$257.30	$257.30
Purchase #4	$102.43	5.472%	$108.035	$108.04	$108.05	$108.00
Purchase #5	$34.47	6.249%	$36.624	$36.62	$36.60	$36.60
Purchase #6	$95.32	10.564%	$105.3896	$105.39	$105.40	$105.40
Purchase #7	$90.82	8.598%	$98.6287	$98.63	$98.65	$98.60
7 purchase totals =	$723.81		$780.5805	$780.59	$780.65	$780.50