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	$171.99	9.849%	$188.9293	$188.93	$188.95	$188.90
Purchase #2	$157.81	6.547%	$168.1418	$168.14	$168.15	$168.10
Purchase #3	$164.50	7.264%	$176.4493	$176.45	$176.45	$176.40
Purchase #4	$73.89	8.281%	$80.0088	$80.01	$80.00	$80.00
Purchase #5	$102.69	11.146%	$114.1358	$114.14	$114.15	$114.10
Purchase #6	$186.93	5.235%	$196.7158	$196.72	$196.70	$196.70
Purchase #7	$17.75	5.316%	$18.6936	$18.69	$18.70	$18.70
7 purchase totals =	$875.56		$943.0744	$943.08	$943.10	$942.90