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	$40.38	6.496%	$43.0031	$43.00	$43.00	$43.00
Purchase #2	$179.78	5.337%	$189.3749	$189.37	$189.35	$189.40
Purchase #3	$133.94	6.380%	$142.4854	$142.49	$142.50	$142.50
Purchase #4	$37.30	13.663%	$42.3963	$42.40	$42.40	$42.40
Purchase #5	$183.83	12.584%	$206.9632	$206.96	$206.95	$207.00
Purchase #6	$22.97	8.433%	$24.9071	$24.91	$24.90	$24.90
Purchase #7	$113.65	8.836%	$123.6921	$123.69	$123.70	$123.70
7 purchase totals =	$711.85		$772.8221	$772.82	$772.80	$772.90