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	$156.29	13.149%	$176.8406	$176.84	$176.85	$176.80
Purchase #2	$138.48	7.209%	$148.463	$148.46	$148.45	$148.50
Purchase #3	$94.50	6.698%	$100.8296	$100.83	$100.85	$100.80
Purchase #4	$59.44	13.502%	$67.4656	$67.47	$67.45	$67.50
Purchase #5	$36.89	4.707%	$38.6264	$38.63	$38.65	$38.60
Purchase #6	$158.85	5.798%	$168.0601	$168.06	$168.05	$168.10
Purchase #7	$204.99	5.169%	$215.5859	$215.59	$215.60	$215.60
7 purchase totals =	$849.44		$915.8712	$915.88	$915.90	$915.90