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	$25.66	11.773%	$28.681	$28.68	$28.70	$28.70
Purchase #2	$24.41	11.583%	$27.2374	$27.24	$27.25	$27.20
Purchase #3	$47.88	10.551%	$52.9318	$52.93	$52.95	$52.90
Purchase #4	$50.86	5.645%	$53.731	$53.73	$53.75	$53.70
Purchase #5	$173.63	3.554%	$179.8008	$179.80	$179.80	$179.80
Purchase #6	$69.89	12.553%	$78.6633	$78.66	$78.65	$78.70
Purchase #7	$81.47	6.691%	$86.9212	$86.92	$86.90	$86.90
7 purchase totals =	$473.80		$507.9665	$507.96	$508.00	$507.90