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	$249.60	10.358%	$275.4536	$275.45	$275.45	$275.50
Purchase #2	$113.96	5.123%	$119.7982	$119.80	$119.80	$119.80
Purchase #3	$39.33	5.366%	$41.4404	$41.44	$41.45	$41.40
Purchase #4	$159.67	12.651%	$179.8699	$179.87	$179.85	$179.90
Purchase #5	$90.26	6.336%	$95.9789	$95.98	$96.00	$96.00
Purchase #6	$173.38	4.610%	$181.3728	$181.37	$181.35	$181.40
Purchase #7	$57.92	13.194%	$65.562	$65.56	$65.55	$65.60
7 purchase totals =	$884.12		$959.4758	$959.47	$959.45	$959.60