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	$180.82	12.627%	$203.6521	$203.65	$203.65	$203.70
Purchase #2	$227.39	13.645%	$258.4174	$258.42	$258.40	$258.40
Purchase #3	$114.43	11.521%	$127.6135	$127.61	$127.60	$127.60
Purchase #4	$96.49	9.661%	$105.8119	$105.81	$105.80	$105.80
Purchase #5	$127.27	4.337%	$132.7897	$132.79	$132.80	$132.80
Purchase #6	$105.94	13.199%	$119.923	$119.92	$119.90	$119.90
Purchase #7	$48.31	7.166%	$51.7719	$51.77	$51.75	$51.80
7 purchase totals =	$900.65		$999.9795	$999.97	$999.90	$1,000.00