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	$11.73	13.667%	$13.3331	$13.33	$13.35	$13.30
Purchase #2	$179.34	6.553%	$191.0922	$191.09	$191.10	$191.10
Purchase #3	$109.67	3.735%	$113.7662	$113.77	$113.75	$113.80
Purchase #4	$238.40	9.331%	$260.6451	$260.65	$260.65	$260.60
Purchase #5	$201.55	8.556%	$218.7946	$218.79	$218.80	$218.80
Purchase #6	$97.54	13.843%	$111.0425	$111.04	$111.05	$111.00
Purchase #7	$87.35	13.271%	$98.9422	$98.94	$98.95	$98.90
7 purchase totals =	$925.58		$1,007.6159	$1,007.61	$1,007.65	$1,007.50