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	$162.89	13.868%	$185.4796	$185.48	$185.50	$185.50
Purchase #2	$142.43	4.308%	$148.5659	$148.57	$148.55	$148.60
Purchase #3	$92.60	7.680%	$99.7117	$99.71	$99.70	$99.70
Purchase #4	$241.87	5.705%	$255.6687	$255.67	$255.65	$255.70
Purchase #5	$75.90	5.725%	$80.2453	$80.25	$80.25	$80.20
Purchase #6	$68.89	9.233%	$75.2506	$75.25	$75.25	$75.30
Purchase #7	$11.49	7.379%	$12.3378	$12.34	$12.35	$12.30
7 purchase totals =	$796.07		$857.2596	$857.27	$857.25	$857.30