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	$30.77	6.808%	$32.8648	$32.86	$32.85	$32.90
Purchase #2	$175.44	5.346%	$184.819	$184.82	$184.80	$184.80
Purchase #3	$20.56	5.243%	$21.638	$21.64	$21.65	$21.60
Purchase #4	$52.77	5.124%	$55.4739	$55.47	$55.45	$55.50
Purchase #5	$242.65	5.479%	$255.9448	$255.94	$255.95	$255.90
Purchase #6	$45.60	5.146%	$47.9466	$47.95	$47.95	$47.90
Purchase #7	$231.79	6.688%	$247.2921	$247.29	$247.30	$247.30
7 purchase totals =	$799.58		$845.9792	$845.97	$845.95	$845.90