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	$95.98	10.144%	$105.7162	$105.72	$105.70	$105.70
Purchase #2	$80.48	12.713%	$90.7114	$90.71	$90.70	$90.70
Purchase #3	$78.51	4.271%	$81.8632	$81.86	$81.85	$81.90
Purchase #4	$55.33	8.641%	$60.1111	$60.11	$60.10	$60.10
Purchase #5	$11.67	5.823%	$12.3495	$12.35	$12.35	$12.30
Purchase #6	$77.75	5.480%	$82.0107	$82.01	$82.00	$82.00
Purchase #7	$135.59	7.631%	$145.9369	$145.94	$145.95	$145.90
7 purchase totals =	$535.31		$578.6990	$578.70	$578.65	$578.60