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	$225.86	12.762%	$254.6843	$254.68	$254.70	$254.70
Purchase #2	$148.54	13.332%	$168.3434	$168.34	$168.35	$168.30
Purchase #3	$189.34	5.437%	$199.6344	$199.63	$199.65	$199.60
Purchase #4	$117.58	4.835%	$123.265	$123.27	$123.25	$123.30
Purchase #5	$52.87	5.105%	$55.569	$55.57	$55.55	$55.60
Purchase #6	$224.92	12.602%	$253.2644	$253.26	$253.25	$253.30
Purchase #7	$73.32	12.271%	$82.3171	$82.32	$82.30	$82.30
7 purchase totals =	$1,032.43		$1,137.0776	$1,137.07	$1,137.05	$1,137.10