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	$100.76	11.645%	$112.4935	$112.49	$112.50	$112.50
Purchase #2	$22.61	8.342%	$24.4961	$24.50	$24.50	$24.50
Purchase #3	$221.56	6.710%	$236.4267	$236.43	$236.45	$236.40
Purchase #4	$136.90	3.186%	$141.2616	$141.26	$141.25	$141.30
Purchase #5	$143.93	5.846%	$152.3441	$152.34	$152.35	$152.30
Purchase #6	$223.71	13.332%	$253.535	$253.54	$253.55	$253.50
Purchase #7	$18.38	9.243%	$20.0789	$20.08	$20.10	$20.10
7 purchase totals =	$867.85		$940.6359	$940.64	$940.70	$940.60