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	$40.94	7.124%	$43.8566	$43.86	$43.85	$43.90
Purchase #2	$136.66	5.160%	$143.7117	$143.71	$143.70	$143.70
Purchase #3	$59.95	3.301%	$61.9289	$61.93	$61.95	$61.90
Purchase #4	$45.28	13.582%	$51.4299	$51.43	$51.45	$51.40
Purchase #5	$73.84	11.417%	$82.2703	$82.27	$82.25	$82.30
Purchase #6	$62.25	7.744%	$67.0706	$67.07	$67.05	$67.10
Purchase #7	$166.69	10.683%	$184.4975	$184.50	$184.50	$184.50
7 purchase totals =	$585.61		$634.7655	$634.77	$634.75	$634.80