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	$99.74	8.663%	$108.3805	$108.38	$108.40	$108.40
Purchase #2	$43.70	11.285%	$48.6315	$48.63	$48.65	$48.60
Purchase #3	$49.92	7.758%	$53.7928	$53.79	$53.80	$53.80
Purchase #4	$114.77	4.369%	$119.7843	$119.78	$119.80	$119.80
Purchase #5	$179.35	9.664%	$196.6824	$196.68	$196.70	$196.70
Purchase #6	$117.77	9.513%	$128.9735	$128.97	$128.95	$129.00
Purchase #7	$100.60	3.311%	$103.9309	$103.93	$103.95	$103.90
7 purchase totals =	$705.85		$760.1759	$760.16	$760.25	$760.20