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	$132.58	6.706%	$141.4708	$141.47	$141.45	$141.50
Purchase #2	$238.67	12.733%	$269.0599	$269.06	$269.05	$269.10
Purchase #3	$231.55	12.243%	$259.8987	$259.90	$259.90	$259.90
Purchase #4	$196.29	13.272%	$222.3416	$222.34	$222.35	$222.30
Purchase #5	$116.29	13.180%	$131.617	$131.62	$131.60	$131.60
Purchase #6	$191.90	8.568%	$208.342	$208.34	$208.35	$208.30
Purchase #7	$43.50	7.333%	$46.6899	$46.69	$46.70	$46.70
7 purchase totals =	$1,150.78		$1,279.4199	$1,279.42	$1,279.40	$1,279.40