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	$56.58	5.182%	$59.512	$59.51	$59.50	$59.50
Purchase #2	$148.79	10.604%	$164.5677	$164.57	$164.55	$164.60
Purchase #3	$129.39	13.145%	$146.3983	$146.40	$146.40	$146.40
Purchase #4	$62.78	7.156%	$67.2725	$67.27	$67.25	$67.30
Purchase #5	$203.32	10.755%	$225.1871	$225.19	$225.20	$225.20
Purchase #6	$49.28	7.643%	$53.0465	$53.05	$53.05	$53.00
Purchase #7	$163.72	4.202%	$170.5995	$170.60	$170.60	$170.60
7 purchase totals =	$813.86		$886.5836	$886.59	$886.55	$886.60