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	$128.60	11.631%	$143.5575	$143.56	$143.55	$143.60
Purchase #2	$164.71	10.836%	$182.558	$182.56	$182.55	$182.60
Purchase #3	$129.50	10.855%	$143.5572	$143.56	$143.55	$143.60
Purchase #4	$91.47	12.827%	$103.2029	$103.20	$103.20	$103.20
Purchase #5	$140.48	7.480%	$150.9879	$150.99	$151.00	$151.00
Purchase #6	$42.28	7.371%	$45.3965	$45.40	$45.40	$45.40
Purchase #7	$187.96	6.780%	$200.7037	$200.70	$200.70	$200.70
7 purchase totals =	$885.00		$969.9637	$969.97	$969.95	$970.10