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	$237.34	12.249%	$266.4118	$266.41	$266.40	$266.40
Purchase #2	$141.85	10.324%	$156.4946	$156.49	$156.50	$156.50
Purchase #3	$125.85	6.305%	$133.7848	$133.78	$133.80	$133.80
Purchase #4	$150.43	5.223%	$158.287	$158.29	$158.30	$158.30
Purchase #5	$80.50	9.634%	$88.2554	$88.26	$88.25	$88.30
Purchase #6	$114.86	12.648%	$129.3875	$129.39	$129.40	$129.40
Purchase #7	$82.64	8.781%	$89.8966	$89.90	$89.90	$89.90
7 purchase totals =	$933.47		$1,022.5177	$1,022.52	$1,022.55	$1,022.60