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	$169.69	9.303%	$185.4763	$185.48	$185.50	$185.50
Purchase #2	$94.39	9.711%	$103.5562	$103.56	$103.55	$103.60
Purchase #3	$233.27	8.380%	$252.818	$252.82	$252.80	$252.80
Purchase #4	$45.50	12.326%	$51.1083	$51.11	$51.10	$51.10
Purchase #5	$99.49	9.194%	$108.6371	$108.64	$108.65	$108.60
Purchase #6	$50.78	11.347%	$56.542	$56.54	$56.55	$56.50
Purchase #7	$173.27	4.677%	$181.3738	$181.37	$181.35	$181.40
7 purchase totals =	$866.39		$939.5117	$939.52	$939.50	$939.50