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	$121.84	4.537%	$127.3679	$127.37	$127.35	$127.40
Purchase #2	$233.70	8.251%	$252.9826	$252.98	$253.00	$253.00
Purchase #3	$80.48	10.590%	$89.0028	$89.00	$89.00	$89.00
Purchase #4	$114.66	10.401%	$126.5858	$126.59	$126.60	$126.60
Purchase #5	$165.48	5.396%	$174.4093	$174.41	$174.40	$174.40
Purchase #6	$36.93	9.757%	$40.5333	$40.53	$40.55	$40.50
Purchase #7	$158.35	5.510%	$167.0751	$167.08	$167.10	$167.10
7 purchase totals =	$911.44		$977.9568	$977.96	$978.00	$978.00