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	$157.73	12.538%	$177.5062	$177.51	$177.50	$177.50
Purchase #2	$195.25	10.828%	$216.3917	$216.39	$216.40	$216.40
Purchase #3	$78.72	13.779%	$89.5668	$89.57	$89.55	$89.60
Purchase #4	$185.73	11.258%	$206.6395	$206.64	$206.65	$206.60
Purchase #5	$108.68	13.706%	$123.5757	$123.58	$123.60	$123.60
Purchase #6	$203.30	6.767%	$217.0573	$217.06	$217.05	$217.10
Purchase #7	$22.96	9.856%	$25.2229	$25.22	$25.20	$25.20
7 purchase totals =	$952.37		$1,055.9601	$1,055.97	$1,055.95	$1,056.00