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	$75.57	9.637%	$82.8527	$82.85	$82.85	$82.90
Purchase #2	$147.50	12.795%	$166.3726	$166.37	$166.35	$166.40
Purchase #3	$182.98	8.418%	$198.3833	$198.38	$198.40	$198.40
Purchase #4	$68.63	5.773%	$72.592	$72.59	$72.60	$72.60
Purchase #5	$127.86	7.650%	$137.6413	$137.64	$137.65	$137.60
Purchase #6	$10.49	8.599%	$11.392	$11.39	$11.40	$11.40
Purchase #7	$17.85	5.603%	$18.8501	$18.85	$18.85	$18.90
7 purchase totals =	$630.88		$688.0840	$688.07	$688.10	$688.20