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	$137.77	6.106%	$146.1822	$146.18	$146.20	$146.20
Purchase #2	$151.53	8.675%	$164.6752	$164.68	$164.70	$164.70
Purchase #3	$233.67	4.642%	$244.517	$244.52	$244.50	$244.50
Purchase #4	$74.64	9.732%	$81.904	$81.90	$81.90	$81.90
Purchase #5	$190.87	5.180%	$200.7571	$200.76	$200.75	$200.80
Purchase #6	$81.67	5.454%	$86.1243	$86.12	$86.10	$86.10
Purchase #7	$90.25	4.404%	$94.2246	$94.22	$94.20	$94.20
7 purchase totals =	$960.40		$1,018.3844	$1,018.38	$1,018.35	$1,018.40