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	$11.96	8.358%	$12.9596	$12.96	$12.95	$13.00
Purchase #2	$238.41	8.779%	$259.34	$259.34	$259.35	$259.30
Purchase #3	$105.93	10.128%	$116.6586	$116.66	$116.65	$116.70
Purchase #4	$80.66	6.157%	$85.6262	$85.63	$85.65	$85.60
Purchase #5	$89.32	5.743%	$94.4496	$94.45	$94.45	$94.40
Purchase #6	$35.58	9.299%	$38.8886	$38.89	$38.90	$38.90
Purchase #7	$214.98	8.658%	$233.593	$233.59	$233.60	$233.60
7 purchase totals =	$776.84		$841.5156	$841.52	$841.55	$841.50