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	$66.27	7.667%	$71.3509	$71.35	$71.35	$71.40
Purchase #2	$178.63	8.542%	$193.8886	$193.89	$193.90	$193.90
Purchase #3	$204.89	12.783%	$231.0811	$231.08	$231.10	$231.10
Purchase #4	$198.77	10.495%	$219.6309	$219.63	$219.65	$219.60
Purchase #5	$70.37	5.629%	$74.3311	$74.33	$74.35	$74.30
Purchase #6	$156.52	7.800%	$168.7286	$168.73	$168.75	$168.70
Purchase #7	$43.57	12.179%	$48.8764	$48.88	$48.90	$48.90
7 purchase totals =	$919.02		$1,007.8876	$1,007.89	$1,008.00	$1,007.90