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	$79.31	8.226%	$85.834	$85.83	$85.85	$85.80
Purchase #2	$121.47	10.699%	$134.4661	$134.47	$134.45	$134.50
Purchase #3	$100.51	7.698%	$108.2473	$108.25	$108.25	$108.20
Purchase #4	$123.85	9.844%	$136.0418	$136.04	$136.05	$136.00
Purchase #5	$86.79	7.708%	$93.4798	$93.48	$93.50	$93.50
Purchase #6	$137.31	9.722%	$150.6593	$150.66	$150.65	$150.70
Purchase #7	$84.61	9.672%	$92.7935	$92.79	$92.80	$92.80
7 purchase totals =	$733.85		$801.5218	$801.52	$801.55	$801.50