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	$93.29	8.126%	$100.8707	$100.87	$100.85	$100.90
Purchase #2	$87.71	6.358%	$93.2866	$93.29	$93.30	$93.30
Purchase #3	$179.36	3.541%	$185.7111	$185.71	$185.70	$185.70
Purchase #4	$222.53	8.687%	$241.8612	$241.86	$241.85	$241.90
Purchase #5	$18.93	3.209%	$19.5375	$19.54	$19.55	$19.50
Purchase #6	$43.53	5.829%	$46.0674	$46.07	$46.05	$46.10
Purchase #7	$84.31	6.579%	$89.8568	$89.86	$89.85	$89.90
7 purchase totals =	$729.66		$777.1913	$777.20	$777.15	$777.30