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	$47.39	8.407%	$51.3741	$51.37	$51.35	$51.40
Purchase #2	$204.72	9.527%	$224.2237	$224.22	$224.20	$224.20
Purchase #3	$30.63	3.362%	$31.6598	$31.66	$31.65	$31.70
Purchase #4	$114.86	6.727%	$122.5866	$122.59	$122.60	$122.60
Purchase #5	$113.50	9.789%	$124.6105	$124.61	$124.60	$124.60
Purchase #6	$137.30	11.768%	$153.4575	$153.46	$153.45	$153.50
Purchase #7	$78.92	13.319%	$89.4314	$89.43	$89.45	$89.40
7 purchase totals =	$727.32		$797.3436	$797.34	$797.30	$797.40