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	$29.49	8.529%	$32.0052	$32.01	$32.00	$32.00
Purchase #2	$217.53	7.363%	$233.5467	$233.55	$233.55	$233.50
Purchase #3	$189.98	11.385%	$211.6092	$211.61	$211.60	$211.60
Purchase #4	$10.26	11.372%	$11.4268	$11.43	$11.45	$11.40
Purchase #5	$150.58	11.746%	$168.2671	$168.27	$168.25	$168.30
Purchase #6	$102.70	13.328%	$116.3879	$116.39	$116.40	$116.40
Purchase #7	$23.87	13.199%	$27.0206	$27.02	$27.00	$27.00
7 purchase totals =	$724.41		$800.2635	$800.28	$800.25	$800.20