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	$238.34	8.709%	$259.097	$259.10	$259.10	$259.10
Purchase #2	$155.52	5.699%	$164.3831	$164.38	$164.40	$164.40
Purchase #3	$9.96	5.381%	$10.4959	$10.50	$10.50	$10.50
Purchase #4	$113.45	4.208%	$118.224	$118.22	$118.20	$118.20
Purchase #5	$82.65	3.301%	$85.3783	$85.38	$85.40	$85.40
Purchase #6	$164.59	6.535%	$175.346	$175.35	$175.35	$175.30
Purchase #7	$41.71	12.324%	$46.8503	$46.85	$46.85	$46.90
7 purchase totals =	$806.22		$859.7746	$859.78	$859.80	$859.80