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	$117.25	12.137%	$131.4806	$131.48	$131.50	$131.50
Purchase #2	$46.61	12.724%	$52.5407	$52.54	$52.55	$52.50
Purchase #3	$179.34	6.465%	$190.9343	$190.93	$190.95	$190.90
Purchase #4	$249.34	10.808%	$276.2887	$276.29	$276.30	$276.30
Purchase #5	$134.66	7.631%	$144.9359	$144.94	$144.95	$144.90
Purchase #6	$225.70	9.679%	$247.5455	$247.55	$247.55	$247.50
Purchase #7	$51.63	9.651%	$56.6128	$56.61	$56.60	$56.60
7 purchase totals =	$1,004.53		$1,100.3385	$1,100.34	$1,100.40	$1,100.20