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	$105.43	5.726%	$111.4669	$111.47	$111.45	$111.50
Purchase #2	$78.46	11.319%	$87.3409	$87.34	$87.35	$87.30
Purchase #3	$181.55	10.547%	$200.6981	$200.70	$200.70	$200.70
Purchase #4	$250.39	13.366%	$283.8571	$283.86	$283.85	$283.90
Purchase #5	$229.81	3.688%	$238.2854	$238.29	$238.30	$238.30
Purchase #6	$9.31	12.335%	$10.4584	$10.46	$10.45	$10.50
Purchase #7	$172.44	9.275%	$188.4338	$188.43	$188.45	$188.40
7 purchase totals =	$1,027.39		$1,120.5406	$1,120.55	$1,120.55	$1,120.60