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	$179.26	4.546%	$187.4092	$187.41	$187.40	$187.40
Purchase #2	$231.64	10.732%	$256.4996	$256.50	$256.50	$256.50
Purchase #3	$10.37	6.409%	$11.0346	$11.03	$11.05	$11.00
Purchase #4	$59.87	13.445%	$67.9195	$67.92	$67.90	$67.90
Purchase #5	$79.83	13.615%	$90.6989	$90.70	$90.70	$90.70
Purchase #6	$21.35	10.856%	$23.6678	$23.67	$23.65	$23.70
Purchase #7	$250.69	13.555%	$284.671	$284.67	$284.65	$284.70
7 purchase totals =	$833.01		$921.9006	$921.90	$921.85	$921.90