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	$164.72	9.594%	$180.5232	$180.52	$180.50	$180.50
Purchase #2	$29.98	7.441%	$32.2108	$32.21	$32.20	$32.20
Purchase #3	$59.63	4.458%	$62.2883	$62.29	$62.30	$62.30
Purchase #4	$51.49	8.488%	$55.8605	$55.86	$55.85	$55.90
Purchase #5	$226.99	6.796%	$242.4162	$242.42	$242.40	$242.40
Purchase #6	$177.98	12.638%	$200.4731	$200.47	$200.45	$200.50
Purchase #7	$28.99	11.441%	$32.3067	$32.31	$32.30	$32.30
7 purchase totals =	$739.78		$806.0788	$806.08	$806.00	$806.10