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	$99.61	10.244%	$109.814	$109.81	$109.80	$109.80
Purchase #2	$39.44	11.478%	$43.9669	$43.97	$43.95	$44.00
Purchase #3	$66.40	6.165%	$70.4936	$70.49	$70.50	$70.50
Purchase #4	$127.66	8.827%	$138.9285	$138.93	$138.95	$138.90
Purchase #5	$189.46	4.844%	$198.6374	$198.64	$198.65	$198.60
Purchase #6	$41.59	10.732%	$46.0534	$46.05	$46.05	$46.10
Purchase #7	$71.78	9.609%	$78.6773	$78.68	$78.70	$78.70
7 purchase totals =	$635.94		$686.5711	$686.57	$686.60	$686.60