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	$72.58	10.755%	$80.386	$80.39	$80.40	$80.40
Purchase #2	$51.27	5.649%	$54.1662	$54.17	$54.15	$54.20
Purchase #3	$234.25	10.699%	$259.3124	$259.31	$259.30	$259.30
Purchase #4	$167.43	8.611%	$181.8474	$181.85	$181.85	$181.80
Purchase #5	$23.72	5.648%	$25.0597	$25.06	$25.05	$25.10
Purchase #6	$66.93	6.764%	$71.4571	$71.46	$71.45	$71.50
Purchase #7	$102.53	5.657%	$108.3301	$108.33	$108.35	$108.30
7 purchase totals =	$718.71		$780.5589	$780.57	$780.55	$780.60