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	$17.36	8.275%	$18.7965	$18.80	$18.80	$18.80
Purchase #2	$239.31	7.202%	$256.5451	$256.55	$256.55	$256.50
Purchase #3	$19.51	8.457%	$21.16	$21.16	$21.15	$21.20
Purchase #4	$29.34	6.127%	$31.1377	$31.14	$31.15	$31.10
Purchase #5	$82.89	7.372%	$89.0007	$89.00	$89.00	$89.00
Purchase #6	$129.89	10.552%	$143.596	$143.60	$143.60	$143.60
Purchase #7	$29.30	5.798%	$30.9988	$31.00	$31.00	$31.00
7 purchase totals =	$547.60		$591.2348	$591.25	$591.25	$591.20