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	$159.65	11.594%	$178.1598	$178.16	$178.15	$178.20
Purchase #2	$33.29	13.177%	$37.6766	$37.68	$37.70	$37.70
Purchase #3	$216.59	11.839%	$242.2321	$242.23	$242.25	$242.20
Purchase #4	$38.92	12.622%	$43.8325	$43.83	$43.85	$43.80
Purchase #5	$57.64	7.854%	$62.167	$62.17	$62.15	$62.20
Purchase #6	$189.58	13.524%	$215.2188	$215.22	$215.20	$215.20
Purchase #7	$45.80	6.828%	$48.9272	$48.93	$48.95	$48.90
7 purchase totals =	$741.47		$828.2140	$828.22	$828.25	$828.20