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	$62.56	4.566%	$65.4165	$65.42	$65.40	$65.40
Purchase #2	$171.32	4.678%	$179.3343	$179.33	$179.35	$179.30
Purchase #3	$249.65	12.403%	$280.6141	$280.61	$280.60	$280.60
Purchase #4	$146.25	11.810%	$163.5221	$163.52	$163.50	$163.50
Purchase #5	$57.72	7.330%	$61.9509	$61.95	$61.95	$62.00
Purchase #6	$9.74	10.501%	$10.7628	$10.76	$10.75	$10.80
Purchase #7	$14.52	3.359%	$15.0077	$15.01	$15.00	$15.00
7 purchase totals =	$711.76		$776.6084	$776.60	$776.55	$776.60