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	$134.89	6.494%	$143.6498	$143.65	$143.65	$143.60
Purchase #2	$129.78	13.137%	$146.8292	$146.83	$146.85	$146.80
Purchase #3	$42.47	9.545%	$46.5238	$46.52	$46.50	$46.50
Purchase #4	$163.50	13.800%	$186.063	$186.06	$186.05	$186.10
Purchase #5	$44.75	9.310%	$48.9162	$48.92	$48.90	$48.90
Purchase #6	$169.54	9.820%	$186.1888	$186.19	$186.20	$186.20
Purchase #7	$37.95	13.718%	$43.156	$43.16	$43.15	$43.20
7 purchase totals =	$722.88		$801.3268	$801.33	$801.30	$801.30