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	$10.64	12.403%	$11.9597	$11.96	$11.95	$12.00
Purchase #2	$248.30	6.541%	$264.5413	$264.54	$264.55	$264.50
Purchase #3	$87.51	12.438%	$98.3945	$98.39	$98.40	$98.40
Purchase #4	$50.49	12.688%	$56.8962	$56.90	$56.90	$56.90
Purchase #5	$77.43	6.137%	$82.1819	$82.18	$82.20	$82.20
Purchase #6	$194.72	10.714%	$215.5823	$215.58	$215.60	$215.60
Purchase #7	$176.51	4.187%	$183.9005	$183.90	$183.90	$183.90
7 purchase totals =	$845.60		$913.4564	$913.45	$913.50	$913.50