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	$55.82	13.786%	$63.5153	$63.52	$63.50	$63.50
Purchase #2	$166.61	5.601%	$175.9418	$175.94	$175.95	$175.90
Purchase #3	$145.59	13.236%	$164.8603	$164.86	$164.85	$164.90
Purchase #4	$41.39	4.733%	$43.349	$43.35	$43.35	$43.30
Purchase #5	$192.77	8.687%	$209.5159	$209.52	$209.50	$209.50
Purchase #6	$230.81	8.591%	$250.6389	$250.64	$250.65	$250.60
Purchase #7	$5.28	4.356%	$5.51	$5.51	$5.50	$5.50
7 purchase totals =	$838.27		$913.3312	$913.34	$913.30	$913.20