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	$184.34	10.566%	$203.8174	$203.82	$203.80	$203.80
Purchase #2	$51.28	6.471%	$54.5983	$54.60	$54.60	$54.60
Purchase #3	$114.34	11.103%	$127.0352	$127.04	$127.05	$127.00
Purchase #4	$98.66	6.854%	$105.4222	$105.42	$105.40	$105.40
Purchase #5	$165.77	11.452%	$184.754	$184.75	$184.75	$184.80
Purchase #6	$249.89	3.166%	$257.8015	$257.80	$257.80	$257.80
Purchase #7	$113.47	13.137%	$128.3766	$128.38	$128.40	$128.40
7 purchase totals =	$977.75		$1,061.8052	$1,061.81	$1,061.80	$1,061.80