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	$229.76	11.312%	$255.7505	$255.75	$255.75	$255.80
Purchase #2	$24.74	9.367%	$27.0574	$27.06	$27.05	$27.10
Purchase #3	$215.43	10.121%	$237.2337	$237.23	$237.25	$237.20
Purchase #4	$83.83	12.152%	$94.017	$94.02	$94.00	$94.00
Purchase #5	$150.96	5.223%	$158.8446	$158.84	$158.85	$158.80
Purchase #6	$36.72	4.250%	$38.2806	$38.28	$38.30	$38.30
Purchase #7	$113.56	13.493%	$128.8827	$128.88	$128.90	$128.90
7 purchase totals =	$855.00		$940.0665	$940.06	$940.10	$940.10