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	$114.85	3.163%	$118.4827	$118.48	$118.50	$118.50
Purchase #2	$80.55	10.502%	$89.0094	$89.01	$89.00	$89.00
Purchase #3	$89.95	13.679%	$102.2543	$102.25	$102.25	$102.30
Purchase #4	$186.63	13.296%	$211.4443	$211.44	$211.45	$211.40
Purchase #5	$210.88	8.758%	$229.3489	$229.35	$229.35	$229.30
Purchase #6	$162.35	3.526%	$168.0745	$168.07	$168.05	$168.10
Purchase #7	$69.28	4.661%	$72.5091	$72.51	$72.50	$72.50
7 purchase totals =	$914.49		$991.1232	$991.11	$991.10	$991.10