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	$124.63	4.160%	$129.8146	$129.81	$129.80	$129.80
Purchase #2	$85.34	8.410%	$92.5171	$92.52	$92.50	$92.50
Purchase #3	$213.47	7.747%	$230.0075	$230.01	$230.00	$230.00
Purchase #4	$38.66	4.574%	$40.4283	$40.43	$40.45	$40.40
Purchase #5	$39.99	9.684%	$43.8626	$43.86	$43.85	$43.90
Purchase #6	$18.48	11.499%	$20.605	$20.61	$20.60	$20.60
Purchase #7	$39.92	10.256%	$44.0142	$44.01	$44.00	$44.00
7 purchase totals =	$560.49		$601.2493	$601.25	$601.20	$601.20