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	$12.65	8.399%	$13.7125	$13.71	$13.70	$13.70
Purchase #2	$134.60	13.560%	$152.8518	$152.85	$152.85	$152.90
Purchase #3	$31.42	3.623%	$32.5583	$32.56	$32.55	$32.60
Purchase #4	$54.82	12.107%	$61.4571	$61.46	$61.45	$61.50
Purchase #5	$218.63	9.750%	$239.9464	$239.95	$239.95	$239.90
Purchase #6	$56.46	6.180%	$59.9492	$59.95	$59.95	$59.90
Purchase #7	$242.51	5.355%	$255.4964	$255.50	$255.50	$255.50
7 purchase totals =	$751.09		$815.9717	$815.98	$815.95	$816.00