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	$168.72	5.803%	$178.5108	$178.51	$178.50	$178.50
Purchase #2	$52.65	9.247%	$57.5185	$57.52	$57.50	$57.50
Purchase #3	$131.79	11.871%	$147.4348	$147.43	$147.45	$147.40
Purchase #4	$164.85	12.631%	$185.6722	$185.67	$185.65	$185.70
Purchase #5	$35.69	13.448%	$40.4896	$40.49	$40.50	$40.50
Purchase #6	$192.94	7.846%	$208.0781	$208.08	$208.10	$208.10
Purchase #7	$198.34	5.106%	$208.4672	$208.47	$208.45	$208.50
7 purchase totals =	$944.98		$1,026.1712	$1,026.17	$1,026.15	$1,026.20