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	$60.81	12.624%	$68.4867	$68.49	$68.50	$68.50
Purchase #2	$140.77	6.727%	$150.2396	$150.24	$150.25	$150.20
Purchase #3	$239.95	10.496%	$265.1352	$265.14	$265.15	$265.10
Purchase #4	$176.43	5.125%	$185.472	$185.47	$185.45	$185.50
Purchase #5	$233.34	7.326%	$250.4345	$250.43	$250.45	$250.40
Purchase #6	$55.25	13.294%	$62.5949	$62.59	$62.60	$62.60
Purchase #7	$98.57	12.855%	$111.2412	$111.24	$111.25	$111.20
7 purchase totals =	$1,005.12		$1,093.6041	$1,093.60	$1,093.65	$1,093.50