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	$105.80	13.867%	$120.4713	$120.47	$120.45	$120.50
Purchase #2	$43.99	3.156%	$45.3783	$45.38	$45.40	$45.40
Purchase #3	$212.74	12.509%	$239.3516	$239.35	$239.35	$239.40
Purchase #4	$211.86	4.869%	$222.1755	$222.18	$222.20	$222.20
Purchase #5	$48.31	9.358%	$52.8308	$52.83	$52.85	$52.80
Purchase #6	$99.66	5.803%	$105.4433	$105.44	$105.45	$105.40
Purchase #7	$215.71	13.278%	$244.352	$244.35	$244.35	$244.40
7 purchase totals =	$938.07		$1,030.0028	$1,030.00	$1,030.05	$1,030.10