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	$16.85	10.285%	$18.583	$18.58	$18.60	$18.60
Purchase #2	$165.52	6.608%	$176.4576	$176.46	$176.45	$176.50
Purchase #3	$48.55	7.540%	$52.2107	$52.21	$52.20	$52.20
Purchase #4	$97.79	6.270%	$103.9214	$103.92	$103.90	$103.90
Purchase #5	$141.86	4.814%	$148.6891	$148.69	$148.70	$148.70
Purchase #6	$226.53	3.281%	$233.9624	$233.96	$233.95	$234.00
Purchase #7	$70.72	13.786%	$80.4695	$80.47	$80.45	$80.50
7 purchase totals =	$767.82		$814.2937	$814.29	$814.25	$814.40