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	$167.82	6.409%	$178.5756	$178.58	$178.60	$178.60
Purchase #2	$84.52	3.152%	$87.1841	$87.18	$87.20	$87.20
Purchase #3	$103.36	9.847%	$113.5379	$113.54	$113.55	$113.50
Purchase #4	$89.67	11.150%	$99.6682	$99.67	$99.65	$99.70
Purchase #5	$211.46	13.213%	$239.4002	$239.40	$239.40	$239.40
Purchase #6	$53.58	10.615%	$59.2675	$59.27	$59.25	$59.30
Purchase #7	$19.25	5.552%	$20.3188	$20.32	$20.30	$20.30
7 purchase totals =	$729.66		$797.9523	$797.96	$797.95	$798.00