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	$234.88	6.246%	$249.5506	$249.55	$249.55	$249.60
Purchase #2	$174.52	3.695%	$180.9685	$180.97	$180.95	$181.00
Purchase #3	$100.63	6.576%	$107.2474	$107.25	$107.25	$107.20
Purchase #4	$134.27	10.523%	$148.3992	$148.40	$148.40	$148.40
Purchase #5	$121.54	5.204%	$127.8649	$127.86	$127.85	$127.90
Purchase #6	$152.93	10.146%	$168.4463	$168.45	$168.45	$168.40
Purchase #7	$205.59	11.315%	$228.8525	$228.85	$228.85	$228.90
7 purchase totals =	$1,124.36		$1,211.3294	$1,211.33	$1,211.30	$1,211.40