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	$90.29	11.145%	$100.3528	$100.35	$100.35	$100.40
Purchase #2	$103.56	7.581%	$111.4109	$111.41	$111.40	$111.40
Purchase #3	$132.33	5.599%	$139.7392	$139.74	$139.75	$139.70
Purchase #4	$41.30	9.520%	$45.2318	$45.23	$45.25	$45.20
Purchase #5	$172.82	8.385%	$187.311	$187.31	$187.30	$187.30
Purchase #6	$29.74	13.826%	$33.8519	$33.85	$33.85	$33.90
Purchase #7	$208.54	10.446%	$230.3241	$230.32	$230.30	$230.30
7 purchase totals =	$778.58		$848.2217	$848.21	$848.20	$848.20