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	$242.95	3.528%	$251.5213	$251.52	$251.50	$251.50
Purchase #2	$51.78	7.808%	$55.823	$55.82	$55.80	$55.80
Purchase #3	$44.70	9.281%	$48.8486	$48.85	$48.85	$48.80
Purchase #4	$57.50	12.208%	$64.5196	$64.52	$64.50	$64.50
Purchase #5	$24.58	4.780%	$25.7549	$25.75	$25.75	$25.80
Purchase #6	$50.28	4.698%	$52.6422	$52.64	$52.65	$52.60
Purchase #7	$162.90	9.558%	$178.47	$178.47	$178.45	$178.50
7 purchase totals =	$634.69		$677.5796	$677.57	$677.50	$677.50