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	$114.55	12.389%	$128.7416	$128.74	$128.75	$128.70
Purchase #2	$159.30	8.219%	$172.3929	$172.39	$172.40	$172.40
Purchase #3	$107.88	7.591%	$116.0692	$116.07	$116.05	$116.10
Purchase #4	$33.38	8.812%	$36.3214	$36.32	$36.30	$36.30
Purchase #5	$81.37	10.667%	$90.0497	$90.05	$90.05	$90.00
Purchase #6	$58.25	13.710%	$66.2361	$66.24	$66.25	$66.20
Purchase #7	$36.65	12.772%	$41.3309	$41.33	$41.35	$41.30
7 purchase totals =	$591.38		$651.1418	$651.14	$651.15	$651.00