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	$196.59	6.814%	$209.9856	$209.99	$210.00	$210.00
Purchase #2	$234.90	6.376%	$249.8772	$249.88	$249.90	$249.90
Purchase #3	$51.81	4.551%	$54.1679	$54.17	$54.15	$54.20
Purchase #4	$54.57	11.388%	$60.7844	$60.78	$60.80	$60.80
Purchase #5	$90.86	7.222%	$97.4219	$97.42	$97.40	$97.40
Purchase #6	$40.57	6.142%	$43.0618	$43.06	$43.05	$43.10
Purchase #7	$231.47	12.291%	$259.92	$259.92	$259.90	$259.90
7 purchase totals =	$900.77		$975.2188	$975.22	$975.20	$975.30