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	$162.25	3.873%	$168.5339	$168.53	$168.55	$168.50
Purchase #2	$128.53	13.504%	$145.8867	$145.89	$145.90	$145.90
Purchase #3	$9.42	5.344%	$9.9234	$9.92	$9.90	$9.90
Purchase #4	$76.89	6.783%	$82.1054	$82.11	$82.10	$82.10
Purchase #5	$249.34	11.734%	$278.5976	$278.60	$278.60	$278.60
Purchase #6	$87.35	11.831%	$97.6844	$97.68	$97.70	$97.70
Purchase #7	$51.53	9.198%	$56.2697	$56.27	$56.25	$56.30
7 purchase totals =	$765.31		$839.0011	$839.00	$839.00	$839.00