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	$139.63	3.136%	$144.0088	$144.01	$144.00	$144.00
Purchase #2	$135.79	6.636%	$144.801	$144.80	$144.80	$144.80
Purchase #3	$54.66	9.336%	$59.7631	$59.76	$59.75	$59.80
Purchase #4	$105.98	11.733%	$118.4146	$118.41	$118.40	$118.40
Purchase #5	$41.45	5.706%	$43.8151	$43.82	$43.80	$43.80
Purchase #6	$162.45	12.388%	$182.5743	$182.57	$182.55	$182.60
Purchase #7	$126.51	7.755%	$136.3209	$136.32	$136.30	$136.30
7 purchase totals =	$766.47		$829.6978	$829.69	$829.60	$829.70