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	$96.29	12.448%	$108.2762	$108.28	$108.30	$108.30
Purchase #2	$114.47	10.517%	$126.5088	$126.51	$126.50	$126.50
Purchase #3	$94.56	6.483%	$100.6903	$100.69	$100.70	$100.70
Purchase #4	$80.39	10.798%	$89.0705	$89.07	$89.05	$89.10
Purchase #5	$98.68	11.761%	$110.2858	$110.29	$110.30	$110.30
Purchase #6	$206.83	11.615%	$230.8533	$230.85	$230.85	$230.90
Purchase #7	$129.59	9.111%	$141.3969	$141.40	$141.40	$141.40
7 purchase totals =	$820.81		$907.0818	$907.09	$907.10	$907.20