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	$250.95	11.850%	$280.6876	$280.69	$280.70	$280.70
Purchase #2	$61.39	9.192%	$67.033	$67.03	$67.05	$67.00
Purchase #3	$230.78	10.370%	$254.7119	$254.71	$254.70	$254.70
Purchase #4	$85.51	10.683%	$94.645	$94.65	$94.65	$94.60
Purchase #5	$28.40	10.789%	$31.4641	$31.46	$31.45	$31.50
Purchase #6	$104.46	10.164%	$115.0773	$115.08	$115.10	$115.10
Purchase #7	$146.87	3.409%	$151.8768	$151.88	$151.90	$151.90
7 purchase totals =	$908.36		$995.4957	$995.50	$995.55	$995.50