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	$241.39	6.300%	$256.5976	$256.60	$256.60	$256.60
Purchase #2	$172.57	12.193%	$193.6115	$193.61	$193.60	$193.60
Purchase #3	$225.84	12.212%	$253.4196	$253.42	$253.40	$253.40
Purchase #4	$75.29	4.505%	$78.6818	$78.68	$78.70	$78.70
Purchase #5	$75.33	3.601%	$78.0426	$78.04	$78.05	$78.00
Purchase #6	$114.68	5.657%	$121.1674	$121.17	$121.15	$121.20
Purchase #7	$41.37	5.608%	$43.69	$43.69	$43.70	$43.70
7 purchase totals =	$946.47		$1,025.2105	$1,025.21	$1,025.20	$1,025.20