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	$56.87	7.548%	$61.1625	$61.16	$61.15	$61.20
Purchase #2	$228.43	3.521%	$236.473	$236.47	$236.45	$236.50
Purchase #3	$53.34	5.851%	$56.4609	$56.46	$56.45	$56.50
Purchase #4	$229.28	12.407%	$257.7268	$257.73	$257.75	$257.70
Purchase #5	$31.71	9.111%	$34.5991	$34.60	$34.60	$34.60
Purchase #6	$143.72	12.851%	$162.1895	$162.19	$162.20	$162.20
Purchase #7	$167.38	3.154%	$172.6592	$172.66	$172.65	$172.70
7 purchase totals =	$910.73		$981.2710	$981.27	$981.25	$981.40