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	$145.31	13.220%	$164.52	$164.52	$164.50	$164.50
Purchase #2	$68.31	6.755%	$72.9243	$72.92	$72.90	$72.90
Purchase #3	$69.69	8.621%	$75.698	$75.70	$75.70	$75.70
Purchase #4	$111.25	9.513%	$121.8332	$121.83	$121.85	$121.80
Purchase #5	$223.33	7.848%	$240.8569	$240.86	$240.85	$240.90
Purchase #6	$6.96	12.832%	$7.8531	$7.85	$7.85	$7.90
Purchase #7	$43.87	7.476%	$47.1497	$47.15	$47.15	$47.10
7 purchase totals =	$668.72		$730.8352	$730.83	$730.80	$730.80