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	$50.70	13.174%	$57.3792	$57.38	$57.40	$57.40
Purchase #2	$222.37	10.214%	$245.0829	$245.08	$245.10	$245.10
Purchase #3	$61.39	10.404%	$67.777	$67.78	$67.80	$67.80
Purchase #4	$174.38	3.593%	$180.6455	$180.65	$180.65	$180.60
Purchase #5	$127.94	10.687%	$141.6129	$141.61	$141.60	$141.60
Purchase #6	$69.32	12.531%	$78.0065	$78.01	$78.00	$78.00
Purchase #7	$190.97	9.149%	$208.4418	$208.44	$208.45	$208.40
7 purchase totals =	$897.07		$978.9458	$978.95	$979.00	$978.90