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	$181.63	12.182%	$203.7562	$203.76	$203.75	$203.80
Purchase #2	$105.67	11.188%	$117.4924	$117.49	$117.50	$117.50
Purchase #3	$29.94	8.529%	$32.4936	$32.49	$32.50	$32.50
Purchase #4	$187.65	6.211%	$199.3049	$199.30	$199.30	$199.30
Purchase #5	$85.99	4.352%	$89.7323	$89.73	$89.75	$89.70
Purchase #6	$223.88	13.732%	$254.6232	$254.62	$254.60	$254.60
Purchase #7	$176.52	3.549%	$182.7847	$182.78	$182.80	$182.80
7 purchase totals =	$991.28		$1,080.1873	$1,080.17	$1,080.20	$1,080.20