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	$242.56	6.823%	$259.1099	$259.11	$259.10	$259.10
Purchase #2	$34.98	10.133%	$38.5245	$38.52	$38.50	$38.50
Purchase #3	$100.54	13.736%	$114.3502	$114.35	$114.35	$114.40
Purchase #4	$213.65	11.429%	$238.0681	$238.07	$238.05	$238.10
Purchase #5	$250.65	10.827%	$277.7879	$277.79	$277.80	$277.80
Purchase #6	$51.96	8.262%	$56.2529	$56.25	$56.25	$56.30
Purchase #7	$62.46	6.229%	$66.3506	$66.35	$66.35	$66.40
7 purchase totals =	$956.80		$1,050.4441	$1,050.44	$1,050.40	$1,050.60