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	$223.42	10.740%	$247.4153	$247.42	$247.40	$247.40
Purchase #2	$152.49	3.256%	$157.4551	$157.46	$157.45	$157.50
Purchase #3	$164.80	12.628%	$185.6109	$185.61	$185.60	$185.60
Purchase #4	$215.52	6.756%	$230.0805	$230.08	$230.10	$230.10
Purchase #5	$116.50	12.678%	$131.2699	$131.27	$131.25	$131.30
Purchase #6	$250.90	7.771%	$270.3974	$270.40	$270.40	$270.40
Purchase #7	$237.83	8.610%	$258.3072	$258.31	$258.30	$258.30
7 purchase totals =	$1,361.46		$1,480.5363	$1,480.55	$1,480.50	$1,480.60