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	$107.51	6.286%	$114.2681	$114.27	$114.25	$114.30
Purchase #2	$180.79	4.871%	$189.5963	$189.60	$189.60	$189.60
Purchase #3	$89.86	13.523%	$102.0118	$102.01	$102.00	$102.00
Purchase #4	$226.61	3.145%	$233.7369	$233.74	$233.75	$233.70
Purchase #5	$162.56	11.401%	$181.0935	$181.09	$181.10	$181.10
Purchase #6	$223.83	6.755%	$238.9497	$238.95	$238.95	$238.90
Purchase #7	$26.91	11.212%	$29.9271	$29.93	$29.95	$29.90
7 purchase totals =	$1,018.07		$1,089.5834	$1,089.59	$1,089.60	$1,089.50