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	$161.77	11.197%	$179.8834	$179.88	$179.90	$179.90
Purchase #2	$111.72	4.310%	$116.5351	$116.54	$116.55	$116.50
Purchase #3	$148.48	4.386%	$154.9923	$154.99	$155.00	$155.00
Purchase #4	$39.41	9.482%	$43.1469	$43.15	$43.15	$43.10
Purchase #5	$16.33	11.869%	$18.2682	$18.27	$18.25	$18.30
Purchase #6	$30.58	7.310%	$32.8154	$32.82	$32.80	$32.80
Purchase #7	$31.52	5.271%	$33.1814	$33.18	$33.20	$33.20
7 purchase totals =	$539.81		$578.8227	$578.83	$578.85	$578.80