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	$147.38	6.205%	$156.5249	$156.52	$156.50	$156.50
Purchase #2	$126.61	8.484%	$137.3516	$137.35	$137.35	$137.40
Purchase #3	$171.50	11.866%	$191.8502	$191.85	$191.85	$191.90
Purchase #4	$170.58	5.649%	$180.2161	$180.22	$180.20	$180.20
Purchase #5	$226.80	13.193%	$256.7217	$256.72	$256.70	$256.70
Purchase #6	$31.72	7.859%	$34.2129	$34.21	$34.20	$34.20
Purchase #7	$192.43	3.746%	$199.6384	$199.64	$199.65	$199.60
7 purchase totals =	$1,067.02		$1,156.5158	$1,156.51	$1,156.45	$1,156.50