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	$60.45	10.280%	$66.6643	$66.66	$66.65	$66.70
Purchase #2	$89.35	6.458%	$95.1202	$95.12	$95.10	$95.10
Purchase #3	$80.41	12.263%	$90.2707	$90.27	$90.25	$90.30
Purchase #4	$185.64	12.798%	$209.3982	$209.40	$209.40	$209.40
Purchase #5	$42.61	5.201%	$44.8261	$44.83	$44.85	$44.80
Purchase #6	$145.60	10.458%	$160.8268	$160.83	$160.85	$160.80
Purchase #7	$196.34	8.345%	$212.7246	$212.72	$212.70	$212.70
7 purchase totals =	$800.40		$879.8309	$879.83	$879.80	$879.80