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	$240.95	7.786%	$259.7104	$259.71	$259.70	$259.70
Purchase #2	$144.49	9.696%	$158.4998	$158.50	$158.50	$158.50
Purchase #3	$154.62	8.472%	$167.7194	$167.72	$167.70	$167.70
Purchase #4	$142.73	6.765%	$152.3857	$152.39	$152.40	$152.40
Purchase #5	$50.72	12.533%	$57.0767	$57.08	$57.10	$57.10
Purchase #6	$10.55	8.624%	$11.4598	$11.46	$11.45	$11.50
Purchase #7	$73.95	11.543%	$82.486	$82.49	$82.50	$82.50
7 purchase totals =	$818.01		$889.3378	$889.35	$889.35	$889.40