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	$93.47	8.374%	$101.2972	$101.30	$101.30	$101.30
Purchase #2	$165.31	9.664%	$181.2856	$181.29	$181.30	$181.30
Purchase #3	$101.84	11.772%	$113.8286	$113.83	$113.85	$113.80
Purchase #4	$37.94	5.628%	$40.0753	$40.08	$40.10	$40.10
Purchase #5	$90.30	11.282%	$100.4876	$100.49	$100.50	$100.50
Purchase #6	$71.82	12.287%	$80.6445	$80.64	$80.65	$80.60
Purchase #7	$226.55	9.671%	$248.4597	$248.46	$248.45	$248.50
7 purchase totals =	$787.23		$866.0785	$866.09	$866.15	$866.10