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	$41.40	12.381%	$46.5257	$46.53	$46.55	$46.50
Purchase #2	$230.72	10.822%	$255.6885	$255.69	$255.70	$255.70
Purchase #3	$54.72	12.196%	$61.3937	$61.39	$61.40	$61.40
Purchase #4	$90.50	13.226%	$102.4695	$102.47	$102.45	$102.50
Purchase #5	$49.89	4.802%	$52.2857	$52.29	$52.30	$52.30
Purchase #6	$203.30	13.732%	$231.2172	$231.22	$231.20	$231.20
Purchase #7	$62.40	12.561%	$70.2381	$70.24	$70.25	$70.20
7 purchase totals =	$732.93		$819.8184	$819.83	$819.85	$819.80