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	$241.67	6.558%	$257.5187	$257.52	$257.50	$257.50
Purchase #2	$28.36	12.455%	$31.8922	$31.89	$31.90	$31.90
Purchase #3	$124.86	7.145%	$133.7812	$133.78	$133.80	$133.80
Purchase #4	$180.98	4.582%	$189.2725	$189.27	$189.25	$189.30
Purchase #5	$165.99	8.692%	$180.4179	$180.42	$180.40	$180.40
Purchase #6	$189.58	12.695%	$213.6472	$213.65	$213.65	$213.60
Purchase #7	$167.51	13.333%	$189.8441	$189.84	$189.85	$189.80
7 purchase totals =	$1,098.95		$1,196.3738	$1,196.37	$1,196.35	$1,196.30