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	$12.35	8.157%	$13.3574	$13.36	$13.35	$13.40
Purchase #2	$92.59	11.764%	$103.4823	$103.48	$103.50	$103.50
Purchase #3	$38.39	8.746%	$41.7476	$41.75	$41.75	$41.70
Purchase #4	$102.67	11.622%	$114.6023	$114.60	$114.60	$114.60
Purchase #5	$129.54	12.599%	$145.8607	$145.86	$145.85	$145.90
Purchase #6	$173.35	10.310%	$191.2224	$191.22	$191.20	$191.20
Purchase #7	$41.89	10.269%	$46.1917	$46.19	$46.20	$46.20
7 purchase totals =	$590.78		$656.4644	$656.46	$656.45	$656.50