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	$40.84	13.161%	$46.215	$46.22	$46.20	$46.20
Purchase #2	$150.54	9.568%	$164.9437	$164.94	$164.95	$164.90
Purchase #3	$37.58	12.143%	$42.1433	$42.14	$42.15	$42.10
Purchase #4	$9.45	13.323%	$10.709	$10.71	$10.70	$10.70
Purchase #5	$71.36	9.455%	$78.1071	$78.11	$78.10	$78.10
Purchase #6	$162.46	6.469%	$172.9695	$172.97	$172.95	$173.00
Purchase #7	$18.32	13.358%	$20.7672	$20.77	$20.75	$20.80
7 purchase totals =	$490.55		$535.8548	$535.86	$535.80	$535.80